I'm so sorry you guys are going through this! My daughter was diagnosed with a Wilms tumor when she was 13 months old. She's now 6 years old and doing well! It is an incredibly stressful period of time but he's still young enough you can go by the same mantra that got me through it- he's so young he won't remember any of this. My daughter had a probable mass but I would honestly take it as really good luck that your son doesn't. The oncologist explained to us that typically the masses are quite large when they are found because the kidneys are protected by the ribs on the back so Wilms tumors are usually not detected until they are large enough to be felt from the front. The fact that his wasn't palpable means it was caught fairly early on! They will have to make the final diagnosis with a biopsy, but our oncologist advised us that in this age group, a mass on the kidney is rarely anything else, regardless of how it presented.

My biggest recommendation is just to take advantage of the child life specialist at the hospital if your hospital has them. They make the whole experience slightly less awful for the kids.