I used sleeping bags at child care no dramas. Didn't even ask, just told them "here's his sleeping bag, he has one sleep, use this".

Also, I've got grobags - 0.5 tog for summer/hot days. It's what I use when we have the 35+ degree days. We never used muslin ones. The grobags have last exceptionally well. I've replaced the winter ones (being Melbourne that's the one I use the most - 2.5 tog) but the three lighter weight ones have lasted three kids and still going strong.