You could try sewing them onto a demin or leather jacket. If that doesn't interest you, covering something else like a bag, blanket, or scarves would make for unique pieces. I save patches for the worn out knees of pants.
Really anything for a child with several fu patches will work. You might try aiming for a sort of play rug or a blanket. Do the best you can to arrange them on a fabric in a way that would create a picture. It needn't be perfect; a child's imagination can fill in the gaps.
Old patches can be used for many craft projects, including bags made with old blue jeans covered with the patches. If the patches are sentimental they can be sewn onto fabric squares and then made into a memory quilt. Patches are also great additions to scrapbook pages.
The best project to use up old patches is to make a quilt displaying them. If you don't have enough patches for a full-sized quilt, you can always make pillows and categorize the patches. If you can crochet, you can always make sun-catchers or a vest with them by crocheting an edging and linking them together.
You can make interesting patches by painting with fabric paint on your patches then use them as patches or make a collage using a variety of them with different paintings on each. Frame your collage when done.