Thanks for all the responses everyone. Really appreciate it.

I had kind of made my decision this arvo and told DH when he got home that i think i'll just take DS1 and DH could have a day with DS2. That way DS1 can have fun without his little brother trying to tag along and i can then chat and get to know the mum (cause i reckon we'd get along pretty well). If DS2 was to go I'd end up stuck in the baby area (he's only 16months)- which he'd get bored with after a while and even though he is only 16months i think he has an understanding that cake is yummy, but that there may not be enough for him.

I also think this will be the case in any future parties only one gets invited to (depending on where and who it is of course)...will only take the child that was invited...it'll will all even out and the other will have a fun day with daddy (they can go to a theme park or movie).

Once again thanks for your replies- its nice to know what others do. Its funny it had never occurred to me these situations of having only 1 son invited to something would happen- i think i assumed (without realising it until now) that having 2 boys they'd likely to do almost everything together. But it will be good to see them have some fun time without each other.