It's required to have a guide from the local tourist office for the trip to Porte de Non Retour. Make sure to stop and arrange one before you make your way down the slave route.
There are minimal places to stop for the bathroom during the day, so make sure you and the kids go whenever you can. Also, carry a bit of toilet paper, just in case you need a side-of-the-road stop!
Le Musee de la Fondation Zinsou is closed on Mondays, so it's best to visit between Tuesday and Sunday.
It can get quite hot in May and June, so avoid these months if possible. The best time to visit Ouidah is November to January.