I took my 9 year old daughter to Lake Accotink for the maiden voyage of our new tandem Necky Manitou. The lake was a perfect place to break in the new kayak (despite the lower parking lot being closed for Springfield Day).
The lake is small though it has a little feeder river/stream that can be kayaked for approximately 1/4 of a mile. There is a small island in the middle of the lake; you can make a lap around the lake (from the boat launch) which is probably a mile around. The marina/boat launch has a nice, shallow, sandy beach which is perfect for entering/exiting the water.
End of the day, it's a nice small lake and perfect for a starter kayaker to work on their skills on a placid lake. The wildlife is pleasant and the commute is very easy from anywhere in Northern Va.
*Note: this probably isn't the best location if you are an experienced kayaker looking for something more adventuresome...I probably wouldn't have enjoyed it that much without my nine year old who's the best company in the world!
$2 launch fee