It's too bad you can't go for two days...Hotels are very cheap right now on Travelzoo and Orbitz. Make it a weekend...
If not, definitely do not miss Believe, Pets Ahoy and Blue Horizons. Also, take the little ones over to Happy Harbour, it's fun for them. Take their suits too, they can get wet over there.
I would suggest taking some snacks. You can also take water, juice boxes, etc. Especially if you have a stroller to tote it all around in...we used to do that when our girls were younger.
Have fun, it's a blast, we have been passholders since we did not have to pay for our girls to get in. lol!
Take care,
Cheryl