Having just done my 1 year old's 1st Birthday Party last weekend, I can only urge you not to stress out about activities for the little ones. They are usually so shell shocked at the festivities that you can't even get them to complete an activity. I found this to be the case with my 2 year old's party last Fall. I went to such lengths preparing games & activities and they just ran around with each other the whole time and could have cared less about my expectations. UGH!!! There are a few things you could have that parents would have to help with - decorating tiaras and crowns for the royal court. Michael's has great things along the princess line in their foam kits & shapes. I'm in the throws of preparing for a 3 year old Princess Party for next month and found oodles of things for the little ones at Michael's. It's this same crowd that I hope cooperates better this year than last!! The parents (if they aren't to caught up in the socializing) can certainly help decorate the tiaras & crowns - it would make for a lovely group photo at the end of the party! I recently found bubbles in small clear tubes that say "Princess" along the side. My 1 year old is fascinated with bubbles as well as my soon to be 3 year old and my 4 1/2 year old. At this age, you're best to stay away from paints & things you'll just have to excuse yourself from your guests to have to clean up.
Little ones love long ribbons - perhaps you could have something like a May Day Pole with long ribbons the kiddos could wind round & round.
I hope you get some more suggestions. Don't be discouraged from the comments... your great intentions will shine through and it'll be a fabulous celebration. Happy Birthday to your little Princess!