The gluten challenge is usually the same for adults and children: 8-12 weeks for the blood tests and 2-4 weeks for the biopsy. The recommended amount of gluten per day is 1/2 to 4 slices of bread per day with 1-2 slices of bread (or equivalent). Withe such a small one, I'm sure the smaller amounts would be enough.
The genetic tests (DQ2 and DQ8) are positive in 97% of all celiacs, which means that if the genetic tests are negative it just means that celiac disease is unlikely - it can't completely rule out the possibility.
Children have a higher rate of false negative celiac tests. If you end up with negative results and still suspect celiac disease, consider having your little one go gluten-free for 6 or so months anyways. It could be celiac disease, or it could be non-celiac gluten sensitivity (NCGS) for which there are no blood tests.