How old is your LO? Our playgroup is at 9.30 ie exactly at nap time. I figure once a week it's worth just living with the consequences and go. DD really enjoys the interaction with other kids. I just don't stay the whole 2 hours. Today she started getting really cranky so we left at 10.15, I know I'm lucky just living around the corner, but maybe your lo naps in her push chair?
I think it's worth it if not too often.