Toilets are generally at the restaurants. Designated picnic areas are rare on ski slopes, generally you either eat at a restaurant/cafe or take sandwiches and eat in a sheltered spot. For obvious reasons terraces attached to restaurants have "No Picnic" signs.
The restaurants in Western European ski resorts are rarely cheap, particularly in France. Figure around €10 for a plate of spag bol or similar.
Good quality hiking/mountain jackets are perfect for skiing, particularly the types that allow layering ie you just have a shell and wear two thin layers underneath. However always be prepared for the worst and take hat/gloves goggles and sunglasses every day. Wear either the sunglasses or goggles whenever you're outside in the daytime.
Weather can be extremely variable in the Alps - I have had my hair and eyebrows freeze solid in late April and been sunbathing in January. Re the sun take factor 20 as absolute minimum for you and the Mrs, SPF 50+ for the kids, and use it every day particularly on earlobes and nose. Also lip balm.
Helmets can be a good idea for adults - a colleague of mine swears by them and - and are seen more these days. For children they are a must, if only to protect against them smacking each other with awkwardly carried skis.
There may be hiking available, but if the snow cover is good you'll need snow shoes or x-country skis and there may also be designated hiking trails.
This link may help if you've not aready seen it
http://www.lesgets.com/
Finally, however tempting and safe it may look, do not ski off-piste without a qualified guide.
Finally finally, enjoy your holiday.