Just back from Mauritius this weekend. It is the middle of their winter there so the weather is really like a decent British summer (with a few heavy rain showers). It is getting dark by about 5:45 in the evening but still warm enough to wander about in short sleeves most evenings. Take some insect repelent (i picked up a few nasty bites...later so did my daughter...but husband unscathed as usual) and make sure the kids are protected against the sun.
Swimming pools are rarely heated. They are lovely once you are in (think about a baby wetsuit for the kids), the sea is warmer.
All Mauritians are taught French and English at school (speaking Creole at home). They seem able to chop and change between all three without hesitating (even in the markets and small villages). In terms of tourists our hotel was a good mix. Plenty of French, a few Brits with earlier school hols, a few Indians, some South Africans a few locals on family reunions.
Port Louis has pretty gruesome traffic jams, but we were impressed with the general quality of the roads in most parts. There are some nice beaches nearby, I believe.
Restaurants seemed happy to cook something for kids if you asked.
There ought to be plenty of hints and tips on here if you look back. My latest is to use airport lounges if you can. Also, there are plenty of money exchange desks just after customs in arrivals (they offer much better exchange rates than the hotels)
I'm not sure whether you have any influence re airline, but the BA direct flight seemed to be a lot less hassle than trying to deal with sleepy children in Dubai for a couple of hours.
You'll probably end up taking a few taxis. Be sure to be firm about the price to avoid being ripped off.
Aside from the long journey with 2 kids, I'm quite jealous. We're definitely planning to go back if we spot another good deal!