What do folks use for catch lights?

I don't have storage space for bulky lighting equipment. For family photos, most of my lighting is the natural softbox I get from sunlight through large windows. I'd like to have nicer catch lights, however. Any suggestions on good things to use? Compact and mobile are important. Something usable for kid pictures (kids are mobile, so I can't spend a lot of time setting up) would be ideal.

In terms of money, I don't like to spend unnecessarily, but I'm more flexible if it makes a difference. I'm also looking for improvement, more so than perfection.