Anjajavy is a great shout if you get the chance - far more interesting than Mauritius. Equally so is Reunion for that matter - kids can learn about Volcano too.

Sorry to throwing around ideas but a lot of my SA friends hit the islands off Mozambique ahead of Mauritius or the Seychelles. He did wedding in the winelands, safari, 2 days in Dullstroom (Walkersons lodge is SO relaxing) and then headed up to Mozambique. Final option I'd throw into the mix would be Durban - fantastic water park for them at Ushaka, Natal shark board and/or battlefields would be interesting for them close to safari options, and then the Oyster Box is a great hotel and beach.

Lots of fun places in the area. Enjoy!