We are taking a trip to Seattle for 4 days and then driving to Vancouver and staying another 4 days. Where is the best area to stay in both? We want to be central to most of the attractions in the areas.

Well, "best" is subjective of course. What's "best" to one person isn't necessarily "best" to another.

I'd stay downtown in both cities. If you post back with more details - such as budget, number of people, time of year and what sort of attractions you're interested in, then we can give you suggestions.

Our budget for the hotels are under $200 a night, we would like hotel with a pool maybe, we are a party of 4, 2 adults and 2 kids ages 3 and 7. We don't really know what exactly we want to see, anything that is kid friendly.

Anywhere within the downtown core is best suited for you...

not sure (at this particular second without checking out prices) but check out:

The Westin Bayshore
Sutton Place
Sheraton Wall Center
Hyatt
The Metropoliatian

Vancouver has all the big chain hotels so a quick search on hotels.com or other hotel websites will give you a broad range to choose from based on your budget.

personally I think Sutton Place is beautiful - great location, gorgeous view of downtown (and Robson Street), and it might fit in your budget (though you don't mention when you are coming to town).

You might also try Priceline...
I often recommend the Rosellen Suites for families. They are more "apartment" type accomodation, in the West End. But I'm not sure if there's a pool.

Definitely try for something downtown.

Try findfamilyfun.com for suggestions for activities with kids. You'll want to visit Stanley Park and the Aquarium there, maybe the Capilano Suspension Bridge, Lynn Canyon, Granville Island, etc.