Detail from the massive gothic fortress, Palais des Papes.
It's already late, a full day of (more) gardening awaits, so here's a quick bit of what I saw and enjoyed of the Provencal city, former home to Popes and current home to some great restaurants (La Fourchette, Piedoie and L'Essentiel spring to mind, but there are many others) and patissiers (for your own benefit and happiness: please drop in on Puyricard for their renowned calissons, among other treats, if you possibly can).
Clotheswise, if you aren't yet among the converted, try Du Pareil au Meme (DPAM) for kid's clothes only; they have a small shop, very centrally located on Avenue de la Republique in Avignon--think fun, clever and above all inexpensive. Also consider Petit Bateau--soft, soft cotton clothes (for kids and their harried mothers).
Now think of the following as a rough, visual poem to this charming old city. Try deep breathing if you find yourself thinking about the taggers who gleefully deface both newer and older buildings.
Oh, and one last tip: as with so many places in the south of France, you'll love it most in the shoulder season--spring and autumn (avoid the mistral).
The popes spent nearly a century in Avignon; I guess they liked it too.