Lovely walk from Orchard Fields down to the bottom, turn left along the river and you will find the boardwalk and the mosaics. Keep going as far as you wish and come back down Old Maltongate or back along the river. Lots to see, logs to walk on and a nice walk. In wet times, you definitely need wellies and a baby carrier would be the way forward.
There is a lovely new labyrinth in Castle Gardens for little ones to explore too!