Recommendation for kids all-terrain scooter

Hi all. I would like to buy a couple of e-scooters for my 2 boys, ages 8 and 10.
We live in the country so I need something that is all-terrain.
I was hoping someone could recommend a solid scooter to start with as I know we will want to mod them in the future.
Important to us:
-Mod-able solid frame, ideally very commonly modded
-Power to go off-road and appropriately large enough tires to do so
-Replacement parts readily available

Is something like the Razor scooters worth starting with? I think they may have lead-acid batteries that would eventually need to be upgraded but is the frame something worth starting with?
I have welders, plasma cutter and other assorted metal working tools as well as a pretty good understanding of electronics, although not an expert on battery tech other than what I have learned from RC. So I am hoping for something that will get them going right away without having to build from scratch.

Razors aren't a good idea for off roading they're strictly on road little toys except for maybe the rx200 which is "made for offroad" but really isn't good like that. If I were you I would get super scooter like big full suspension scooters with key and light much much better and purpose built for offroading. They are also relatively cheap same ish price as Razor they are cheap chinese remakes all over.