Slightly different criteria here for those on bikes as distance isn't as bad for bikes as on foot but it’s the surface that changes the difficulty. The easy routes are mostly either tarmac or nice flat tramways with the odd navigation element to traverse. If you feel like more of a challenge then why not try The Big Trail.
Moderate trails are not much harder than the easy ones but are the longer trails. They should be able to be done by mum, dad and two children on their bikes.
Much tougher trails over rocky ground, much steeper slopes and more aspects to navigate as you go round. These trails are also the longer ones over the harder ground. Definitely not able to be done by scooter. Care should be taken with youngsters.