Honestly? Home.
A 3 year old can be tough to travel with (been there more than a few times) and you would be surprised what a variety of simple day trips will do...
A local pet store to see puppies and kittens and snakes eating mice. A picnic at a local park with a good play area. A damn good pillow fight on mom and dad's bed.
That's the stuff that will carry you (and them) through with memories.
Just my thinking...anything you get to do with them will be great.
