Well, I mostly used the advice people gave from public comments, especially Glassdoor.
For the most part, everyone was accurate about the group interview. Mine specifically went like this:
It was 7 of us, excluding the manager and HR manager.
We did an icebreaker of introducing ourselves. My Toys R Us manager is a cool guy who games, and the HR is a nice lady that gets us to laugh and relax.
After introductions, they split us into two groups, one of 3 and one of 4. We then had 5 minutes to use mega blocks to build a business. I was with a girl who was blanking out and so nervous (thankfully, even though this was my first interview, I was a lot more confident) and a guy who showed up late, so we barely put together some kind of building and parking lot and called it a bubble business. The other group put together a much more smooth-looking 'car wash'. I guess the HR was trying to see how well we could improvise and how creative we are, as well as dexterous.
After the blocks, we had to blindly pull a random toy out from a bag she passed around. We had to use the information given on the toy boxes and information pamphlets she handed out, and give a short and sweet sales pitch/explanation of the toy (as if we were trying to sell it to a customer).
Finally, we went in one by one to the individual interviews (which were extremely fast and only consisted of getting to know my availability, signing paperwork, and being offered the job). I don't know if they hired everyone there that day, as I was the first to go. They told me that while they hire up to 70 people for the season, they may only keep around 6 people afterwards - so if I am punctual and hard working, I have a chance to stay as part-time or full-time.
So I guess, in short, you should walk in cheerful and more relaxed, and don't sweat about practicing multiple Q&As for their seasonal position. Just stay alert and keep your brain active so you can think of good ideas on the spot. Dress business casual or semi-casual - just make sure you look nice.