Make sure that your little one is feeding as usual. Making sure they have wet diapers is very important. Try and keep them in the shade or indoors as much as possible. You can also put your little one in a luke warn bath or little pool with warm water to help keep them cool. Also, wet some washcloths or rags with cold water and apply frequently to baby's face, neck and feet. Remove any extra padding in the bed to allow for air to circulate. Open windows to create a cross breeze. Fans are useful but dont put them directly on the baby. Hang wet towels over chairs or windows to cool the air. (The evaporating water causes cooling). Keep curtains drawn during the day to prevent the sun from heating up the room. Try not to hold your baby a lot when your outside. It makes you and baby hot. Use a stroller or buggy. They say a sleeper is usually good enough and not to worry about blankets well you can do just the opposite. Have just the diaper and use the blanket. A very light onesie may be good too. They have such delicite skin that you don't want the little rolls they have to get irritated.
Since a babies room is best and they are most comfortable when their room is between 61 and 68 you can put a thermometer in the room so you can keep an eye on it and make sure it isnt to hot. Also, you can check your babies temperature to make sure they are not to hot.
If you feel comfortable going out...the airconditioned car is a saving few minutes out of the heat. You can also go get some things done like grocery shopping. The store is cool and you can have them take a nap while shopping. Also, there are small coffee shops like the Spotted Cow in Mill Creek that are comfortable to just sit, have a lemonade, let them sleep and your 2 year old can play in a little play area with toys.
Here is an article from the seattle PI. http://blog.seattlepi.nwsource.com/greenparenting/archive... It gives some ideas for your home and family.
Hope you find some peace with the weather. I am doing the same things with our 2 month old. If you need someone to talk to I would love to hear from you. God Bless!