After a day or so, he won't be falling over anymore! Amazing how quick they learn at this age.
I would have thought that both Saughton and Roseburn parks would be good for learning on? But do you mean 'cycle path to actually go somewhere'?
From Roseburn park, you are very close to the entrance to the North Edinburgh Path network and it is amazingly easy to cycle to Cramond or the Botanics or Ocean terminal. Those probably sound a bit far away, but I suspect they will all be do-able pretty soon - and they are mostly flat and off-road. Much depends on attitude; when she was younger, my daughter (now 5) cycled 5 miles easily, on a wee bike. She now has a much better bike, but is somewhat more reluctant to ride it <sigh>.
A lot of forumites have 5 year olds, and we've been talking about a group cycle. Maybe when it warms up, we should try a joint expedition to Cramond? Or a meet up at Saughton?