If the four-year-old is still having toileting accidents regularly, or if they wear a pair during the day and then a clean pair to bed, then yes, 37 pairs may not be out of line. (Also, I just went and counted; my youngest kid has about 17-18 pairs in the drawer, and probably a couple more in the laundry. Spouse, the laundry-wrangler and buyer of kids' clothes, is not an excessive spender for the sake of spending.)

But that's beside the point. Unless "37 pairs" means "a lot of underwear (which if someone counted might be less than half that many)", WHAT THE HECK IS THIS GUY DOING COUNTING HIS GRANDDAUGHTER'S UNDERPANTS?