Worms are a good source of liquid, but you could also dip them in water before feeding, for a little extra.
How much have you been feeding? Baby birds have tiny stomachs but are ravenous. Parents will feed small amounts throughout the daylight hours. Could be you're not feeding enough.
It's imports to know what kind of bird it is, so you're giving it the right food. In the wild babies will get a wide range of foods, depending on the species. But I think the wet dog food is a good plan, as it'll be fortified with all the important nutrients for life, just not necessarily in the perfect proportions.
Find a rescue or rehabber and have a good chat with them.