OK, will think about for the boys next bike, his current bike may not have the gearing so I might have to buy him an MTB next year (he's almout grown out of his current bike anyway).
I'm a 100 mile cyclist when fit (though not at the moment), so I think I can manage 3-8 miles at 5% -10% gradients off road in my current low gear (cycled up Beallech na ba, on a 42 front. 25 back), however the point of hillwalking is not to be done in at the foot of the hill, so the cost of a cheap MTB from Halfrauds on Cycle to work (halfords ok if you don't let them build it) might be cheaper than buying a MTB specific groupset and straight handlebars for my commuter.
I'll try once and see how I get on with the boy, but we may both have new bikes next yaer if it proves too difficult/tiring with current set up.
Thanks for advice.