My Little Pony.

Drinking formula or breast milk for children under a certain age. Sharing a bed with parents.

Teletubbies

Any shirt that says "I'm the big brother", "tummy time", inheriting a dying planet and all its many problems with no help whatsoever.

My little pony.

high chairs

Gogurt

There are a lot of things only children would enjoy, that virtually no adults would except maybe those with developmental disabilities or just a really childlike mind, like Barney & Friends for example, but I can't think of anything that's only for children in the sense that adults should be discouraged or prohibited from partaking in it..

My advices.