If I had to choose only one park in Québec City, it would be the Jacques-Cartier Beach Park.
Apart from the sound of the wind in the leaves, the chirping of birds, the swash coming from the St.Lawrence river, this place is the most zen park in Quebec City. A little away from the tourist center of Quebec is an unknown gem.
Bring your chairs and a good book.
Your pots and shovels to entertain the kids on the beach.