Whinlatter blue climbing is concentrated into a couple of longish fire road drags, Gisburn is much easier because the climbs are shorter. There will be a couple of spots where your 6-year-old may be pushing, but they will be shortish.
The Snake is much better now they’ve repaired it. If anything it feels easier the slower you go, as the turns are quite tight at full gas, so should be fine for younger riders now. They’ve got rid of the potentially slippery wooden bridge at the bottom as well.
However, I would personally park at Cocklett Hill rather than the Hub to give your young’un a warm up on easier stuff before you get there.
The rest is pretty much a motorway, very little in the way of tech features, just a couple of tight berms here and there with a bit of bumpy track.