We used Snocool (british company) the past 4 times we've stayed there. They have British instructors who are ACE! We've stay with premiere neige who organise the bookings for our little ones each time. Quick and efficient - especially over peak weeks when numbers are limited.
We have been going at Easter for years and it's always OK. They cannon the upper slopes well. The issue is the lower road, which is often closed about then, but you can still get down another blue and usually the bottom red.