I did this last year with an anime convention during July. Took some time to find the store, it was actually awesome, despite being in their low stock phase of much things. The people there were cool, in within five minutes, without me having to say much, already had a onesie picked out for me. It went something like this.
I was kinda hiding behind daddy, cause kinda shy bab, they guessed I wanted to pink one, and that I wanted the butterfly print. Printed it up, talked for about a good thirty minutes. Funs was had. The second trip there, I spotted a pack of their medium overnights. Daddy was cruel, made me pony up and blushy by making me ask about them. Unfortunately, they were for someone else, but we still left the store again with more onesies. We were asked about the theme of the store a few times, opinions on a few products, and I d'awwwed at the rocking horse they had.
All in all it was a fun time, and I am wanting to go back again. Everyone was friendly and helpful. You can tell they have pride in their product and brand, which I think is key to making it such a positive experience. Just be careful you don't drive past, cause like I said... Chicago.