Go to the coast - your 2 year old will love running and playing in the sand (it can be cool, but it is also very uncrowded.) You can easily do day trips into Olympic National Park and enjoy the rain forest. If you are on a tight-ish budget, see if you can get one of the camping cabins at the state parks on the coast, if your budget is higher - I love to stay at the Seabrook resort. There are lots of great things to do in the mountains - but I found beaches were easier when my kids were little. My personal favorite stretch is from Ocean shores to Pacific Beach - as it gives easy access to the park: https://mapswa.com/discoverwa/#9.58/47.252422/-124.013591