OF COURSE Morgan would put his kids in cute clothes and costumes.
It's already tradition to have cute outfits for kids because he made it up ages ago. It's adorable, fun to make, and if you're the head tailor that the Lamb keeps resurrecting, why not use your position to slowly influence fashion for generations to come.
They grow up so fast that they quickly don't fit anymore, so they are carefully kept and given around for younger babies. Any kid of the cult has been wearing a Lamb onesie, cape or costume at some point in their life.
The amount of cute kid clothes in the cult has tripled since the head tailor had twins and nobody is complaining.