My 7 year old and I stayed in St. Germain and went to at least one different playground a day to keep things interesting. The playground at the Jardin du Luxembourg is for pay, but very nice; Tuileries is great before or after the Louvre; on the way to the Marais, there is the Nelson Mandela park with a PG, one although the one for older kids was closed at the time. I would combine PG with neighborhood wandering as every neighborhood has at least one good PG (e.g. there are at least two in front of the Musee Marmottan, in addition to the huge Bois de Boulogne). We also went to the one in front of Bon Marche. She loved the Eiffel Tower and the bateau mouche at night. At the Louvre, she focused on the Mona Lisa but after that neither of us really wanted to see paintings (I've been several times to the Louvre and we live in Italy) but we really enjoyed the Middle Eastern and Persian archaeological pieces.