Ozark Trail 24" M.1 Mountain Bicycle, 8 Speed, Black, Fits Riders 4'6" - 5'6", Teen, Unisex

Ozark Trail makes quite a few bikes in that size range. I believe all of the 24" bikes are the same bike, just different colors. They would be a good fit for your son. There are 3 different 25.7 small bikes (Timber, Vibe, Ridge). I believe the Ridge is the best of the bunch, and it is also the cheapest, so I didn't bother linking the other 2. Ozark Trail 24" M.1 Mountain Bicycle, 8 Speed, Black, Fits Riders 4'6" - 5'6", Teen, Unisex - Walmart.com 24" Ozark Trail Timber Mountain Bicycle, 8 Speed, Black, Fits Riders 4'6" - 5'6", Teen - Walmart.com Ozark Trail 24" M.1 Mountain Bicycle, 8 Speed, Blue, Fits Riders 4'6" - 5'6", Teen, Unisex, Online Only - Walmart.com Ozark Trail 24" M.1 Mountain Bicycle, 8 Speed, Vanilla, Fits Riders 4'6" - 5'6", Teen, Unisex, Online Only - Walmart.com Ozark Trail 27.5" M.2 Ridge Mountain Bike, Small Frame, Fits Riders 5'0" - 5'6", Blue, Adult, Unisex - Walmart.com

27.5 wheel size is going to be a little too bit big for a 10yo regardless of what the small frame size says. That said, the 24” vibe fits the bill here and is well within the price range: https://www.walmart.com/ip/726164996?sid=582be81e-9cbd-492f-8344-cf70d2924af8 at $212. Upgrade to the adult size when they’re like 13 and getting taller than 5’6”.