You could also look at mini ‘plus’ bikes like the Vitus 20+ (and 24+) as well as the Specialized Riprock. These are very trail friendly with MTB geometry and much bigger tyres, so they ride very well off road. They are also an intermediate size, so a Vitus 20+ is bigger than a Vitus 20 but smaller than a Vitus 24.
The downside is that these are tougher off-road bikes, so heavier than the more ‘hybrid’ style Islas, Frogs, standard Vitus kids etc… but definitely worth a look.
It’s also well worth looking at CycleSprog (website and Facebook) as they are an excellent resource for all things related to riding with kids, and they have lots of reviews of different bikes.