In reply to Bobling: There's a hostel in the village of Le Tour but everywhere will be banked out with skiers in March.I'd say you could do a lot with a 2 year old, especially if they are back packable still. I'd go for it...snow shoeing?
Look at Camping Glacier D'Argentiere (might be open and in good weather temperatures might be reasonable in March) - Jon's the one to advise as he lives in Vallorcine...in fact you could do worse than splash out a little on a snow shoe trip with Hilary, Jon's wife, rather than go up anywhere in a cable car. She has a website...'Hilary alp' or similar.
btw Getting about is no trouble - excellent trains, free if you are camping (and I guess hostelling) in the valley.