Ok so we went last summer with 11 and 9 yo. Too young for canyoning, via ferrata or downhill mountain biking (IMO anyway!). We did hire e bikes and do some flat routes.
MTBs and e bikes are readily available to hire. Also helmets, body armour etc. I believe you can get MTB lessons too, might need to sort these ahead if you want them
We also did:
Rafting - some operators will provide minibus there
Parapente - likewise
High ropes & zipwires across Nyon waterfall - think you can get bus there or it’s a walk
Take a ski lift up and do walks from there. So walk is mostly downhill. Walking routes available from Office du Tourisme. There’s a good lift and walk route to Les Gets, another to Avoriaz. Can use buses to get back to Morzine
Some good restaurants for lunch up the mountain, need to plan around it tho as they are only open strict lunch hours!
Goat village & walk to waterfall, not sure how easy this is without a car. Good restaurants at goat village
Big pool in central Morzine - has a slide but it’s quite slow/tame
Swim in lake Montriond. Beautiful. SUP and kayak also available
Mini golf. One by Montriond, one in Avoriaz
Ice skating - good for a rainy day
Wednesday local food market 😋
Toboggan run in Les Gets - the Morzine one is not attached to the rails and lots of stories about people losing skin on it
Wibit in Les Gets
Various free activities put on by Morzine in the town square - live music, giant board games, craft market etc
Side trips to Annecy and Lake Geneva - def need a car for this though
Tennis - we never quite managed but there are courts available to hire
A lot of stuff is free or cheap if you have the Multipass, €3 per day through your accommodation if they have signed up. So for example the pool is included, ski lifts included, mini golf included, tennis courts included or cheap and ice rink you just pay for boot hire.