Keep the child on a comparable level with the dog. If the child is above the dog (standing) then the dog will want to jump up, naturally, to play. If the child is more at the dog's level (without getting in his face) and playing games which do not involve jumping or running such as tug or fetch the toy, then the dog will not feel the need to jump on your daughter.
There are many threads here on boxers and children. In fact an entire forum category. Use the search engine for more information on how to manage kids and boxers.
Also, the child is more than likely moving away from or backing up from the dog as it is jumping on her, thus making it harder for her to keep her balance. If you can teach her to "take up the space" the dog is jumping in by taking a step TOWARD the dog instead of away from the dog, she has better control over her balance and it will cause the dog to have to divert his landing or fall backwards, which will also deter him from further jumping. No knee in the chest, just simply step into the space where the dog would be landing or into the dog's space as he is jumping. Probably not easy for a child to accomplish, but you can try.
Turning away is also effective. But I think one of the best ways to stop jumping is when the dog jumps, at that VERY INSTANT, end play. Walk away and ignore the dog completely. End the fun right then and there and give the dog no attention for jumping behavior. This shows him he doesn't get what he wants by jumping and therefore, he will stop jumping if there is nothing to be gained by doing so.
Good luck.
