I have a couple Chinese Honda 50 knockoffs that have had no issues over the 10 plus years I have had them but are mainly used by me to give the baby grandkids rides around the yard. My wife and I and even my 250+ pound dad have used them as pit bikes at Oshkosh for many years now. They are not race bikes, but work good for yard play bikes.
Years ago I started my daughters at about 6 and 7 on old Hondas I restored for them... A QA50 (auto) and an MR50 (manual clutch). After a year I moved them up to KX60 and then CR80 race bikes.
I now have also picked up a used Yamaha PW50 for my little grandkids and a KTM 50 race bike in case I can get my oldest grandson more interested in racing.
I would suggest looking for a Honda or (chinese knockoff of Honda) 70 or 110 for FBIII. The 110 would be the smarter bet for his size weight IMO. These are easy bikes to learn to ride on and will be fun for play riding. Obviously they are not "race" bikes, but that can come later if he gets into it. (If you can find one, an older Honda XR75 or XR80 would make a good starter bike also)
Honda 50 knockoff
Daughter's old race bikes
3 wheeler rides for grandkids
Daughter who I started on Honda 50 when 6 years old bought herself this about 12 years later.... Both girls transitioned to manual trans first cars with no issue due to their early years on minibikes then race bikes.
Grandson's first time riding PW50 by himself (about 6 years old) I followed him on one of the Honda 50 knockoffs.
One of my grandaughter's getting her first taste of dirtbikes... Start em young!
