in my mothers group there are about 7 original kids, but nearly everyone has had a second, and two have had a third, and they are all born around Jan/Feb.... there is literally a birthday every week for over 2 months.... its expensive and ridiculous... this year most seemed to have parties with family and friends, and invited us mothers group friends along too and those that wanted to come, came.... sometimes two people had parties on the same day, its just one of those things... you have to do things to suit yourself and your family and whoever can come can come, and those that can't can't.... to be honest i choose the date of my child's party to suit me and my family and i wouldn't really give it a thought if there was a party the day before, i'd probably only worry if it was on the same day..... plus people with small babies can just come for an hour or so if they want....

another idea is to celebrate the childs birthday at your mothers group, so bring a cake etc and sing happy birthday, and just invite family and friends to the actual party, and that also helps keep it smaller...

try to just plan the day for yourself and your child and enjoy it, don't worry about who can come and who can't, as long as your family are there thats the main thing.... to be honest i'd be glad if we all just had parties every 5 years or something, they become such a drag when there are so many people/kids to include...

good luck!