You want a four stroke auto-clutch: XR/CRF50, XR/CRF70, KLX/DRZ110. Yamaha makes some TTR options too, but the electric start is frustrating when the battery doesn't hold a charge and there's no kicker. Not sure how big a 7 year old is, but I would guess a 70 would probably be the best fit for now. These things hold their value too, sure kids outgrow them but there are always new kids, and these things are pretty bulletproof. Just stay away from LBTS adult pit bike toys, and chinese junk.