7 is a hard age. Just depends on the kids size. You are better off to let them ride bicycles till they are ten or 11.
I know you want to. My son rode his first event at 2 1/2 years old on a gas powered motorcycle. He was a big kid. PW 50 YAMAHA, then a Beta 50, 3 different ty 80's. A gas gas 80, to a beta 250, 300 Raga, 250 Sherco, 300 4rt beta 300 RR Trs and now a 300 rr Montesa.
Lots of fun, but I could of just waited till he was 11 or 12 when HE really wanted to ride. He just turned 24 and I just bought a 2021 Beta 80 for my 12 year old grandson. So I put the Beta 80 in my sons name hoping that we can make that bike last until he has a son that will learn on it.
The electrics can be fun at home in the yard but totally suck at an event once the batteries die. FInd a nice condition ty 80 and just let him have fun until he really wants to ride.