How to change toddler responses to "Check Toddler"?

Why didn't you ask on the Discord? There's a help channel there, and there are more active modders on there than over here, especially Mac users who might be able to give better advice on what they do to compensate for the lack of programs. There are no tutorials for your situation unfortunately, other than snippets from Zer0's tutorials going over tests and making interactions that will help a bit. Speaking of Zer0, they do take tutorial requests and you could try asking for one if it's something you'd be interested in. I unfortunately don't have the time right now to write one myself.

You shouldn't need any other programs or tools for this besides S4S and the TDESC Browser (which if you didn't see it in the Discord, now has a Mac version). Basically you want to check the outcomes of the interactions and see how they are structured, and for what you are describing you want test_based outcomes which tests for the situations and results you want. So one outcome of the "Check Toddler" interaction should have a test for the hygiene/etc with a weight (weight controls how likely something will be randomly chosen) and will have a continuation to the diaper or bath request interaction depending on what is chosen. Another outcome will check to see if all needs are above x with another set of weights, then lead to the book or flashcards as you described.

Here's an example from an interaction I quickly grabbed with a search program, file E882D22F!00000000!000000000001864A.oven_AddCombo.InteractionTuning.xml. Notice how it has 3 different potential_outcomes sections, with 2 possible weighted outcomes in each section except for the last one. The TDESC describes potential_outcomes as "If all of the tests pass, the outcomes will be randomly selected based on the provided weight."

The first section says that sims will fail more often based on a weight of 6 vs 4 since they are below the skill level of 2.
The second section says that sims will succeed more often based on a weight of 7 vs 3 because they are between the levels of 3 and 4.
The third section says that sims will always succeed with a weight of 1 (against nothing) once above lvl 5.
You will probably want a similar structure for yours, except you'll be using continuations in the outcomes, testing for the toddler (aka targetsim as subject).
<V n="outcome" t="test_based">
<U n="test_based">
<L n="tested_outcomes">
<U>
<L n="potential_outcomes">
<U>
<U n="outcome">
<V n="animation_ref" t="enabled">
<U n="enabled">
<T n="factory">11675<!--Oven_RecipeActions_AddCombo_Succeed--></T>
</U>
</V>
<L n="loot_list">
<T>11085<!--StatChange_Turns_01--></T>
</L>
</U>
<U n="weight">
<T n="base_value">4</T>
</U>
</U>
<U>
<U n="outcome">
<V n="animation_ref" t="enabled">
<U n="enabled">
<T n="factory">11674<!--Oven_RecipeActions_AddCombo_Fail--></T>
</U>
</V>
<L n="loot_list">
<T>11085<!--StatChange_Turns_01--></T>
</L>
</U>
<U n="weight">
<T n="base_value">6</T>
</U>
</U>
</L>
<L n="tests">
<L>
<V t="skill_test">
<U n="skill_test">
<T n="skill">16701<!--statistic_Skill_AdultMajor_GourmetCooking--></T>
<V n="skill_range" t="threshold">
<U n="threshold">
<U n="skill_threshold">
<E n="comparison">LESS_OR_EQUAL</E>
<T n="value">2</T>
</U>
</U>
</V>
<T n="use_effective_skill_level">True</T>
</U>
</V>
</L>
</L>
</U>
<U>
<L n="potential_outcomes">
<U>
<U n="outcome">
<V n="animation_ref" t="enabled">
<U n="enabled">
<T n="factory">11675<!--Oven_RecipeActions_AddCombo_Succeed--></T>
</U>
</V>
<L n="loot_list">
<T>11085<!--StatChange_Turns_01--></T>
</L>
</U>
<U n="weight">
<T n="base_value">7</T>
</U>
</U>
<U>
<U n="outcome">
<V n="animation_ref" t="enabled">
<U n="enabled">
<T n="factory">11674<!--Oven_RecipeActions_AddCombo_Fail--></T>
</U>
</V>
<L n="loot_list">
<T>11085<!--StatChange_Turns_01--></T>
</L>
</U>
<U n="weight">
<T n="base_value">3</T>
</U>
</U>
</L>
<L n="tests">
<L>
<V t="skill_test">
<U n="skill_test">
<T n="skill">16701<!--statistic_Skill_AdultMajor_GourmetCooking--></T>
<V n="skill_range" t="interval">
<U n="interval">
<U n="skill_interval">
<T n="lower_bound">3</T>
<T n="upper_bound">4</T>
</U>
</U>
</V>
<T n="use_effective_skill_level">True</T>
</U>
</V>
</L>
</L>
</U>
<U>
<L n="potential_outcomes">
<U>
<U n="outcome">
<V n="animation_ref" t="enabled">
<U n="enabled">
<T n="factory">11675<!--Oven_RecipeActions_AddCombo_Succeed--></T>
</U>
</V>
<L n="loot_list">
<T>11085<!--StatChange_Turns_01--></T>
</L>
</U>
<U n="weight">
<T n="base_value">1</T>
</U>
</U>
</L>
<L n="tests">
<L>
<V t="skill_test">
<U n="skill_test">
<T n="skill">16701<!--statistic_Skill_AdultMajor_GourmetCooking--></T>
<V n="skill_range" t="interval">
<U n="interval">
<U n="skill_interval">
<T n="lower_bound">5</T>
<T n="upper_bound">20</T>
</U>
</U>
</V>
<T n="use_effective_skill_level">True</T>
</U>
</V>
</L>
</L>
</U>
</L>
</U>
</V>

My server? If they aren't nice they get the boot. 😂 And the majority of servers I've been in are nice, rarely have I seen an issue but it usually gets taken care of by the mods immediately if there is one.

The TDESC Browser does not search for and extract tuning, it instead tells you what the tuning and everything inside it does so you understand what you are changing and why. I recommend reading Zer0's tutorials on the matter to help you understand how to use and read them: 
www.patreon.com/posts/bonus-tutorial-31960337
www.patreon.com/posts/bonus-tutorial-31988039
www.patreon.com/posts/bonus-tutorial-2-32028544
And I also recommend posting on the download page to let the creator know a search feature to find certain functions would be useful. 

It shouldn't be a full-blown overhaul, aren't you only editing the Check Toddler interaction to continue to the proper toddler responses based on their needs like you were asking about? I'll give it a look later and try to show an example if I find the right files.

That's okay, lol. So there's 2 things you can do, you can either delete that entire section you copied/pasted (and only that section, if you click the little - on the left you can safely collapse sections to highlight and delete without worry). Though there's a <U> tag above that you need to delete too, so collapse that one instead of the <U n="outcome">

The second thing is to replace the <T n="factory">146673<!--socials_Friendly_Toddlers_Hug_Fail--></T> with <T n="factory">146672<!--AnimationElement: socials_Friendly_Toddlers_Hug_Success--></T>. And keep the "FAILURE" to "SUCCESS" you changed.

Are you sure you have the right file? And that you're hitting "Save" when done changing the file? Because either option should have worked (especially the deleting), and if it's not working it's probably the wrong file, or something else. When I did a quick search for other interactions using the "146673<!--socials_Friendly_Toddlers_Hug_Fail-->" animation for toddlers four of them came up, so it's likely that you are editing the wrong one.

E882D22F!00000000!000000000002661A.si_touching_Toddler_Apologize.InteractionTuning.xml
E882D22F!00000000!0000000000023EA5.si_touching_Toddler_Comfort.InteractionTuning.xml
E882D22F!00000000!0000000000023CF9.si_touching_Toddler_Hug.InteractionTuning.xml
E882D22F!00000000!0000000000025C49.si_touching_Toddler_ShareTheLove.InteractionTuning.xml

Since you hate that animation you should probably edit all of them anyhow.

The only masterlist is the TDESC I'm afraid. I explained weights previously, but from what I understand reading the TDESC and my previous knowledge, it's saying that outcome has a multiplier base_value of 1000 and is more likely than anything else to occur (since it seems EA did lower numbers for everything else). The base_value increases by the multiplier number shown (in this case 0, so no increasing) when the multiplier's test passes (one of the tests being at the sims owned house).

To find this section in the TDESC you'd open up Interactions > find the regular Interactions again > Outcome > Test_Based > Tested_Outcomes > Potential_Outcomes > Weight and there you will see the base value and multipliers.

For the bladder just copy the 16652 number (the tuning ID) and either use XML File Finder program or the Extract Tuning option from S4S to open it, the min and max value is listed around line 122. Zer0 has tutorials on commodities now if you need more info.
<T n="max_value_tuning">100</T>
<T n="maximum_auto_satisfy_time">1440</T>
<T n="min_value_tuning">-100</T>

It's mostly trial and error for removing stuff, but the vast majority of things can be removed without issue if you make sure to delete the section properly. Like you want to remove the test_set, which is fine to remove. The only files you need to be completely careful with when deleting stuff is SimDatas, but since they are all different it's hard to explain what can and cannot be deleted.

Oh darn, sorry for the late reply, this got lost after I got sick. You can find them in 03B33DDF!00000000!2B5DB22CD6E0B83E.postures.Tuning.xml. I recommend getting DocFetcher or a similar program to type in keywords and find what you're looking for.