[mommyofcam]

We live near the Dells and frequent the area for fun often. I would recommend a stroller actually. It's nice to have somewhere to set the kids while all of you can enjoy people watching when not in the water. They can sit easier in a stroller to enjoy a snack and you know there not roaming around near deep water or slipping on the wet floor. Plus, if you go walking around to shop, it is a must. Traffic can be horrible, so keeping them safe is key.
I would highly recommend life jackets. Your 3yr old especially can walk around in a wading pool area (if the hotel offers one) while you hold or sit down with the baby. If you go into a deep pool, kids seem to like to be able to float (and that causes you less work)!
One more note. They do sell these inner tube devices that blow up you can set a by inside of. Probably around $8.00 at Target/Walmart. They inflate easy and pack nice in a suitcase!
Do you know where your staying? I can comment on snacks and such based on that.
p.s - if you get a chance, take the kids to Paul Bunyan Cook Shanty. It is a MUST! Everything served "log camp buffet" style right at your table. Picnic tables, metal cups/plates, fun atmosphere and GREAT food!