ditto, either that or for real towpath riding go to caverham and ride allong the bridlepaths to mapleduram, pangbourne, etc then (if theyr fit but inexperienced) do a loop on the bridleways through the chilterns.
I wouldn't worry, much as lots of people think they'r rad-core-tothemax-dudes, in reality even my mum can ride follow the dog at cannock in under an hour.
The freshers rides at uni often involved poeple coming out for the first time on supermarket specials, we usualy went through ecalshall, up potters clough, over redmires, down the packhorse/plantation run off stanage then back up and over to do blaca moor and ride back into the town center.
Are you intending to turn them into MBR readers who'll ride 6" bikes arround the home counties?
*no such thing in the South east.
:-p