You might be surprised.
Half day lessons. Do mornings, as although it's a faff to get them out, it's all done by lunchtime, and you can then have a play afternoon.
Les Arcs is fantastic. There's tobogganing in both 2000 and 1800 villages. There's a pool with a slide in 1800, the Museum of Mountain Animals over in Peisey-Vallandry, and the Light Show at the top of the Varet lift in 2000. Though to be honest, my youngest (now 10, but aged 6 when he learned to ski), is happy just playing in the snow for an afternoon.
I'd stay in 1800 personally, somewhere with a pool.
There's a fab green run in 1800, and that's where they'll do a good chunk of their beginner week. It has ginant hands to high five, arches to ski through, and xylophones that you play with your poles. It's open to the public, too, so you and the DC could lap it in the afternoons. It's then a fun activity.
Go for a ski school that specialises in small groups (we used Evolution2 in 1800). They run all lessons in English and have a maximum group size of 8.