I had earlier posted a reply, and now it`s gone...
Anyway , I was saying that since the party is towards the end of September, a fall or Halloween theme for decorating might be fun. Cupcakes could be decorated by providing white, orange and black toppings etc...
If weather permits, scavenger hunt would also be a good idea as would be a good old fashioned game of kick baseball (soccer baseball using a big beach ball )
Since the birthday girls mentionned bike riding , how about a min olympic sort of afternoon with differant stations set up that are more appropriate for this age group.
- egg race
-potato sack race
-wheel barrow race (where one person has the legs held by the partner as they race)
-3 egged race
The good old fashioned sorta games. Having a few adults to co-ordinate the events .