The worst thing about playgroup/mothers group etc is comparing. It's really hard not to, but its' important to realise that all bubs are different and it doesn't mean anything is wrong. Wait until they're sitting, crawling, walking etc, there's always a few that are later and the mums worry. It's not worth it. If you're worried, see your early childhood centre and they will probably tell you all is normal. Just try not to compare.
Having a 7 year old, i can tell you I don't remember much at all about her as a baby, but at the time, when she laughed, crawled, rolled etc was all important. Now she's in school, you wouldn't know which was the kids that crawled first, talked first etc, because they can all do it now!!!! I try to remember this with my second and just let her develop how she wants. And this time, i'd rather she take her time!! It all goes to fast..