La Vanille Crocodile Park on the s coast is good as an'attraction' sort of place, of which there are not many in Mauritius.
A day trip to Grand Bassin in the centre of the island - it is a fantastic temple- or many temples in a beautiful mountain setting, and a huge, unimaginably huge, statue. The temples are very welcoming to tourists, just be prepared to take your shoes off. Brilliant view of the volcanic mountain interior from the Hanuman temple up the little mountain peak in the centre.
En route or afterward the other sites in this area are the Black River Gorge viewpoint and the Chamerel area - Chamerel falls -v spectacular. The whole Black River Gorge area, and especially the drive down from the top to Black River on the W coast.
Get a ferry from Trou d'eau Douce to Ile aux serfs
Mahebourg and Vieux port is interesting, good historical information about the battles.
The east coast and the south are the most beautiful parts, IMO.
Do try the fantastic and extremely cheap street food from vans and stalls - little samosas, (mild), gateau piment, , bel phoori, farata, (like a roti, with a filling). Food all v safe to eat I Mauriuts. And the ready peeled tiny pineapples to eat whole.
Personally I wouldn't be trekking a 3 yo to port Louis or Grande Baie from the E coast. Traffic, over development etc.
The S Coast road is lovely, from Souillac to Les Mornes.