Slider door. It does have a lock on it, and I found it difficult to open up. I'm not sure if all the sliders are as hard to open. I would think it would be hard for a 3 year to do this. Maybe others w/ kids can comment.
Definitely dead bolt, and put up the chain, a 3 year old shouldn't be that tall to keep every one in at night.
The kitchen has several cabinet doors. I know I've seen the kid proof things that go on the outside of the doors. Here is a link to the ones I was thinking about.
http://www.diynetwork.com/diy/lv_safety/article/0,2041,DIY_14130_2276466,00.html
Cabinet lock - less than $3 each. Features a button on the side and one on the front that must be pressed simultaneously to release the serrated plastic strips. To use, slide the strips through cabinet handles, then through the lock and secure.
I remember at least 2 sets of 2 cabinet doors in the 2 bedroom. There may have been 1 more. Maybe someone has a pic, to know for sure.
There are several drawers in the kitchen and around the 1 bedroom, I'm not sure if you are locking those as well. Specifically the onese w/ silverware and knives in the kitchen.
Good luck, and have great trip