Double sibling party?

Not sure there's a lot of traffic here, but here goes. My two kids have birthdays 15 days apart. I'd like to have ONE party for both. It will be #1's third b-day and #2's 1st. Since the baby doesn't have any friends yet, all the guests will be friends of big sis. I certainly don't expect people to buy a gift for the 1 year old that they may not know well or at all. How do I convey this on an invitation? Or do I at all? I know it's tacky to mention gifts on an invite, but how do I do it? Ant suggestions are appreciated! Thanks!

I probably wouldn't mention gifts at all, people will usually do what they want to, regardless of what the invitation says. I think its great to do a double party for the two of them. :)

I second not mentioning gifts.

What is the theme of the party going to be?