So at New Year, we did the Monsal trail and Carsington Water. We're planning to do some of the Tissington Trail and Manifold valleys at Easter. DS is on a bike and can do a reasonable ride but doesn't like hills (he's only 4 so bike has no gears). DD is in a bike trailer aka The Queen of Sheba.
Any other ideas? Don't have to be in Derbyshire - we're a couple of hours away from there but happy to travel a bit for a weekend trip. Planning trips further afield in school holidays so even recommendations as far as Scotland welcome. As DS is only 4-5, then the majority of the route (i.e. 99%) needs to be on off road cycle path. Very quiet country roads OK if for short distance.