I recently bought a tag along bike for my son. Despite his initial resistance to anything cycling after a quick whizz around the block he was calling out faster daddy, faster and weeee! I'm taking the bikes down to Surrey this weekend but don't expect to see me grunting and hauling him up some dirt track on Leith Hill (not yet anyway).
There are few easy (read as flat) routes to choose from nearby. The Downs Link being one, it's a disused railway line for most part, and then there's the Wey navigation/Arun canal. Both off road, which is fine as I have to get used to having twelve kilos of trailer and the added weight of a five year old tagged on the back.
Only hope the weather improves.