Not thinking that no one could ever possibly be good enough for her children. I am apparently not good enough for dp despite the fact we have been together 15 years, but then neither have any of the perfectly pleasant men sil has brought home either. Mil has ended more than one sil's relationships bbecause sil's bf/partner has been so wholly unwelcomed and outright ridiculed by mil.
It's quite sad really.
I have a ds and although he is still very young, I hope that I don't behave like my mil when he gets himself a partner. As long as he is happy whoever he goes out with is good enough as far as I am concerned, with obvious exceptions like violent criminals etc.
Other than that I think, offer help if you can provide it. Don't say you can help then don't.
When dc are tiny babies, the advice around newborns will probably have changed, and the parents will probably be following whatever that advice is. Trust their judgement with their dc and don't interfere. You have had your turn it's theirs now.
When buying dc presents, please, please, please consider the size of the house they live in, the available space and the practically of what you are buying.
Yes it would be lovely if dc could have a full size fuseball table, a giant Tracey Island, a play Fort, tent and five foot Teddy bear. But they live in a two bed terraced house with both parents, where exactly are they supposed to put those lovely gifts?
Don't take it upon yourself to do ANY 'first', of any description. Especially with a first born. Especially especially when that first born is very likely to be an only. It is absolutely not your place to take that from the parents. Ask by all means, but expect a no.
Generally just try not to be an interfering know it all tit. Mum (and dad) really do know best. Remember you are neither.