This is fun for all ages- older kids will like making the rockets, designing their own modifications and colours and younger ones or small brothers ad sisters have a blast watching them take off.
Here is one site that has instructions to make your own , they has several diffrent kinds of bottle rockets and some were easier to make than others. Our group made ones similar to these- water bottle rockets
Our group made both 2L and smaller ones. Basic supplies are : bristol board duct tape, a hand bicycle pump ( one with needle) , cork and small plywood board.
Tons of fun- the rockets really took off !