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I learnt to ski in montchavin which is 200m down the hill from les coches. We were warned that the blues down into montchavin were really reds but the local tourist board had classed them as blues so beginners weren't put off.
Must admit I always took the cable car back to montchavin. But there were nice, flatter areas at the top of the cable car.
Be aware that the altitude isn't the highest so at the end of the season the snow might be sparse.
Definitely ring them - this is just the kind of question you need to ask the people who've been to all the resorts. They'll be able to recommend somewhere suitable for your specific requirements accommodation-wise too. Each family has their own particular needs and with skiing being such an expensive holiday you want to make sure it's as 'right' as it can be. These small, specialised companies pride themselves on their tailor-made care, so let them advise you.
Reberty is sort of Les Menuires isn't it? I have skied there and wouldn't recommend for a beginner. Lift pass expensive and you won't use much of it. Also the run back to resort gets busy and is more of a red than a blue if I recall correctly.
I don't know the other places. I have lots of ideas on where (in S French Alps) would work for beginners though....