Especially if it's off-season and even moreso if your kid is lefty. I'm a lefty myself, and am STILL kicking myself for not getting the adult lefty catchers mitt I saw at one in NC when I had the chance. NOBODY has lefty catchers mitts for adults. Even though I doubt I'd ever need it, there's still the chance my little guy gets good enough that it'd come in handy for his practice.
They've usually got a lot of masks, batting helmets and the like as well, all four 1/2 to 3/4 off retail. If you're looking for a glove for a 6yo to grow into, that's a good place, because they often end up with excess in-between gloves, because when a parent is getting a glove for a 10yo, they will often do what you're doing, and buy an adult size for their kid to grow into, so retailers don't sell the mid-sizes as well.
Fun stuff getting the boys into baseball. Good luck!