Hi Martin, I’ve just gone through this upgrade with my (almost) 5yo daughter, from a Cnoc14 to a Beinn20 small. It really doesn’t feel like a heavy bike in the hand, she’s so much more confident on it already, the bigger wheels really help. She’s almost got the hang of the gears already, needing a prompt when to change but has expanded the terrain that can be handled so very little pushing or towing required. Plus the metallic blue of hers is stunning.
Looking back I should have put her on a bigger bike sooner!
I’d say don’t over think it, kids will battle on regardless, colour is more important!!😃
Alternatives, I’d look at the Frog models, I think they’re a bit lighter.
Hth.