Some people are adamant that we should use only natural fibers. They do love their soapboxes, don’t they? One person I had the questionable pleasure of interacting with made it sound as if we should all be wearing wool undies, anything else is hazardous to your health.
Acrylic will melt, yes. I’ve not looked in the baby section of stores lately but I expect a lot of the items sold are made of synthetics. If the adults are reasonably responsible with their care of babies and small children it’s unlikely any harm will come to a child wearing synthetic fabrics.
I use all cotton for washrags and dishrags. Some people like some synthetic in the mix. I think wool would either stretch too much when wet or felt with use, maybe both.
If acrylic yarn won’t dry when wet I guess you better not wash it, ever.