Witches have a 1/300 chance of spawning as a foal. If you find one there is a 142% chance that it will be adorable

src/main/java/com/minelittlepony/model/ponies/ModelWitchPony.java

@@ -30,6 +30,7 @@ public class ModelWitchPony extends ModelZebra {
         super.updateLivingState(entity, pony);
         EntityWitch witch = ((EntityWitch) entity);
 
+        isChild = entity.getUniqueID().getLeastSignificantBits() % 300 == 0;
         leftArmPose = ArmPose.EMPTY;
         rightArmPose = witch.getHeldItemMainhand().isEmpty() ? ArmPose.EMPTY : ArmPose.ITEM;
     }