Ok so strictly speaking this is cheating as we did this walk up the Simonside Hills WITHOUT the kids, but we passed several families on route, some with babies in rucksacks and others with older children scrambling around the rocks. It’s worth the climb, which is not really too strenuous as the views are just breathtaking. There’s tales to tell en route of mythical dwarves and neolithic carvings to look out for on the unusual shaped crags (although I didn’t realise cavemen could carve i luv kev)? And most importantly the most perfect picnic spots sheltered behind the rocks looking out to panoramic views across to the Cheviots. Just beautiful.
We followed this walk, but there are other shorter ones too from the carparks http://www.theaa.com/walks/the-ancient-spirit-of-the-simonsides-420345
http://www.forestry.gov.uk/forestry/englandnorthumberlandrothburysimonside