My kids are great on their pedal bikes. Both of them have over a year of riding in and have lots of control. Hell, they go mountain biking with me almost every weekend in the summer and go everywhere I go. They go thru creeks and shit at south park just fine.
I think the problem they are going to have is getting used to holding up more weight compared to the pedal bike and controllong the gas. I would not let them use coaster brakes when learning how to ride a pedal bike, they had to use the hand brakes. So hopefully that comes easy.