They’re basically kids saddles. They’re used a lot in RDA sessions as it provides extra support and security for the child
I bought a cub saddle for my daughter when she was around 18 months old. It was okay and got her out of the basket saddle she'd been 'riding' in previously. They don't really have a form to them, they're just a step up from a felt pad tbh. They don't give children much security or seat, but as I say they're fine for just being led around in-hand.
My daughter rode in hers for a few months but once I started riding out with her (ponying her pony alongside my horse) I felt that a proper made saddle was what was necessary to help her advance so I had a gorgeous custom made leather saddle made and she must have ridden in that saddle till she was around 10 or 11 years old I guess.
So, for a short term, slow speed riding thing, they're fine but faster work, no I wouldn't have a whole lot of faith in them.