Convert custom adult hair to toddler hair

Make a copy of the file in an easy to find location (like your desktop)
Go into S4S and find the file and open it
Export the mesh
Go back to the main menu> CAS> Create 3D mesh and pick one of the toddler hairs that is closest to your mesh
Export the mesh from the EA hair
Open up the default toddler hair mesh and hit Shift+F1
When the append section opens find the mesh from the adult hair you want to convert and click it (don't double click), when you click once it should open the library, go to object and look for the one called "S4Studio_mesh" Shift click all of the mesh pieces that start with S4Studio and then click "Link/Append from library"

It should plop the mesh into the same window as the toddler hair. Delete the toddler hair and then scale down the adult hair to fit the head. Once it's done hit save and import the mesh into the package file of the EA toddler hair.

Now just drop it into your game and test!

As a note though, A lot of clay hairs have a scalp/face edge around the mesh, this won't fit the toddler head. Obviously people have found a wa around this with all the toddler conversions thus far, but I gave up on it personally. Alpha hairs however do not usually have that so they convert really fast.
If you are converting alpha hair make sure that when you're viewing the package for your hair you go to tools>modding> Glass shaders