If you want to take that on, decide if you want to use Sims 4 Studio and Blender or CASTools and Milkshape, and look up some beginner tutorials.
For the ears and horns, you'll need to modify the mesh to make it smaller and lower it to the heads of children and toddlers. The face paint might or might not work on a child or toddler without modification.
You can open the package in either CASTools or Sims 4 Studio and change the ages it's valid for.
