I've been told by Rosewood's US operations that Mexican law prohibits children in diapers and pullups are not permitted in organized childcare. All of the Rosewood hotels in Mexico with childcare have a statement to this effect on their website. I have asked whether having a babysitter would permit them to use the kids club space and told no, it is not permitted under the law for children in diapers to be in the physical space of an organized childcare facility.

I only took a quick look at the Melia's website, but they state that they provide babysitting for children four and under. They might make a distinction that complies with the law, Rosewood might be misinforming me, I really don't know more than this though.