How did you get the chain off? If it's loose enough to just push it off track, it's probably too loose and could stand to lose a link. But I don't ride toddler bikes so I don't have a lot of experience with those and the overall chain length may be too short. A mechanic will want all the pieces in the same place, or they risk multiple visits. A mechanic will also have a bunch of spare links around that have like zero monetary value but come in really handy sometimes.
Find a GOOD bike shop. Not just a big one, or the one with the most expensive bikes in the window (run away), but one that sells used bikes and probably has some hippies working there. Bring the whole toddler bike in and explain the situation to the mechanic. They can probably fix in in 5 minutes. If they are nice enough, they might even do it for free. (but even hippies gotta eat, so they might still charge you. don't be offended)
Alternatively you can purchase a new bike chain, a bike chain tool (make sure and get one that's the right size for the chain), and watch some youtube videos and spend probably an hour of your own time trying to make it right. Working with bike chains takes a little bit of experience, and a little bit of voodoo. You might not get it right on the first try. Or the second try. And if you don't know how to do it correctly, you'll just keep messing up forever. So don't have too much hubris.