http://www.brambleski.com - toppest of top end chalet companies.
Lessons are too much for 2.5yr old, if they have snow club or somewhere they can play in the snow and have creche facilities this is much better. At that age they can't stand up on skis and they get cold and exhausted. The kids' club option means they get used to being bundled up, being in snow and sliding about on it.
You'll probably find ski schools won't take them that early anyway and will suggest the kids' club/creche option.
I know from experience, I live in the Alps with 2 small children, and 2.5 is too wee! (BTW Bramble Ski is not my company, in case anyone thinks I'm pulling a fast one and advertising!)
Happy holidays.