Absolutely no problem at all; indeed they should be allowed for definite.
A while back, someone I know parked in a Child space as a disabled one was not available, and she was literally screamed at by an aggressive 30-something chav with a kid who 'needed' the space.
'You don't look disabled, just fat!' he yelled at my friend. 'Get of that f-ckng space!' She refused and said 'if you are THAT bothered, go tell a security guard in the store. Or tell the manager. If I am not meant to be here, he will make me move.'
She defended herself, but was very shaken by the situation. She has a chronic illness and has a blue badge as she struggles with her mobility sometimes.
Child spaces are only courtesy spaces, and I am pretty sure that even people who are not disabled and don't have kids, can still park in there. There is no 'law' attached to them.
Shockingly, the man did not go into the store; he just hurled more abuse and drove off out of the car park altogether!
I believe firmly, that the people with the babies now, who feel entitled to these spaces, and who kick off when someone parks in them, are the ones who, 10-15 years ago, used to park in the spaces themselves! (Their 'entitled-to' attitude tells me this!)