I could really use a way to tow another bike with my bike. For a challenge, it will usually be a kids bike, so I can't assume the top bar will be on the same level as mine. I'm sure some of you must have done this. So what works?

Now, I've seen my bike shop guy ride a bike while holding onto another bike next to him, but it didn't look that easy or stable, so I'd rather just tow it. I was thinking about some kind of rack mount that would hold the other bike's front tire on the rear rack, with its rear tire trailing along behind, kind of like a tag-along. Any reason this wouldn't work?

Other ideas? I suppose a trailer would help too, but I don't have one yet.