Reunion / Mauritius
 

First trip to Reunion and Mauritius planned for July. Return flights from/to Europe into St Denis Reunion but hoping to also go across to Mauritius. I'd like suggestions about how best to split the trip? We are a couple in 40s with an 8 year old. He'd love to see the volcano and 'kids attractions' but he probably won't manage any lengthy hiking etc. Budget isn't fully set and would consider anything that looks fun! Suggested things to do, time split between destinations and accommodation options all welcome! Thanks :)

I would recommend you to do Réunion first and Mauritius last. Indeed, Réunion is more nature/hiking and not so much a beach destination, while Mauritius is primarily a beach destination. How long is your entire trip ?

Thanks - 11 full days there, with travel on the adjacent days either end. We arrive on the Air France evening flight and return on the morning flight. I think we would plan to return to Reunion for at least one full day before travelling home to avoid stress, but not fixed on that.

It's safe indeed to return to RUN max the evening before. Knowing this and with a 8 y.o. kid, I would do 5 days in each, or 6 days Réunion / 4 days Mauritius. Of course, rental car is needed on both islands.
For accommodation, in Réunion, you could split your stay in 2 different places : one in/around St Denis and the other one in the south. In Mauritius, I have always stayed at Sofitel in Flic-en-Flac (west coast) and it was lovely. But there are tons of nice laces over there.