Well, Toulouse is on the Canal du Midi, and if you are into canals, marinas etc, then there are a few interesting little places nearby. It's also where Rick Stein filmed a trip down the canal to the sea in the south a couple of years ago:
Castelnaudary, south of Toulouse. Has a lovely marina area and is also a nice little town.
North of Toulouse there are Montech, Castelsarassin and Moissac, all on the canal and all really nice. Also there is Montauban, not on the canal du Midi, but a nice town again. Moissac is very nice with an Abbey which you can visit and a nice centre; just outside of Montech is the Pente d'Eau, a whole different type of lock and very interesting to watch: picture HERE.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.