Since the museum belongs to the city of Paris, the permanent collections are freely accessible and definitely worth a visit for the whole family.
If you're looking for a nice place to have some tea or coffee after your visit, I strongly recommand you go to the Swedish Institute nearby (11 rue Payenne), where you can relax in a lovely old courtyard (and they have very reasonnable prices).
To reach the Musée Carnavalet from Ivry, simple take subway line 7 and get off at Pont Marie, from here it's a lovely ten minutes walk along old streets to the museum.


