Unless, your kids are riding on PRIVATE property, (yours or someone who gives you written permission to do so), your kids can't be legally riding on crown or maintained trails. The off road vehicle act states that they MUST be at least 12 years of age. It is the same with ATV's. Sleds also have a minimum age for a person to operate them.
Yes you can get insurance stating your the rider, BUT if your kids are riding and crash the insurer will void the policy and not cover anything, plus then you will have to answer yes whenever buying insurance and get asked have you ever had a policy canceled before. If they get stopped on crown land, (OPP S.A.V.E. team and conservation officers patrol areas on ATV's, then you will get ticketed, and depending upon the circumstances they can even seize the bike.
Not saying your kids can't shouldn't ride, just advising of the potential issues. Might want to rethink the idea unless you have a few acres for them to ride on. It gets really boring riding around a 1 acre loop.
Maybe I misunderstand the exceptions stated in the law.
Age limit for driving
4. (1) No owner of an off-road vehicle shall permit a child under the age of twelve to drive the vehicle. R.S.O. 1990, c. O.4, s. 4 (1).
Exception
(2) Subsection (1) does not apply where the child is driving the vehicle,
(a) on land occupied by the vehicle owner; or
(b) under the close supervision of an adult. R.S.O. 1990, c. O.4, s. 4 (2).
Wouldn't exception (b) negate the age restriction?