No, you shouldn't. People are going to be carrying around very hot drinks, and if your toddler runs into them or trips them up, someone could be badly scalded. It is not a sensible or safe place to allow a child to run around - and it is pretty annoying for other patrons too.
Note - I am NOT saying parents of toddlers shouldn't go to cafes, but I am saying that they should act with consideration for other people in the cafe. Everyone should act with consideration.