Another vote for Esprit or Mark Warner.
We’ve used them several times and whilst not cheap, our girls (7 & 5) have always enjoyed themselves. They aren’t cheap, but then skiing isn’t. This year, the lessons, childcare, ski hire and lift passes cost more than the holiday basic price.
As for the ESF, we’ve used them independently in Morzine and as part of a package with Esprit.
In Morzine last year, our eldest was in a group of 20 with 1 instructor, and she could barely understand his English. This year in Belle Plagne with Esprit, she was in a group of 8 (max group size) with an instructor who spoke excellent English. She enjoyed it much more this year and made lots of progess.