Tips for daytrips close to Helsinki

We're looking to spend a short week exploring around Helsinki this February, maybe renting a car. We have two kids under 5, so are looking to balance being on the road and sightseeing with anything interactive and entertaining for the kids. (Since it's a family outing we'll leave the more sporty activities like skating and skiing for when they can both enjoy it).

I hear Fiskars is nice, but to leave Hanko for summer.
Any tips or ideas?

And particularly if you have tips for good or convenient places to eat en route, so we can skip the Hesburger for something more nutricious ;)

Thanks so much!
Jessica

If you don't want to go skiing or skating, summer really would be a better time for trips like this.

Indoor places: Hvitträsk in Kirkkonummi.

Thanks citizen1!
For those of you considering, I found out it's closed during Feb, but this website does show other options of castles and manors that are also worth viewing: http://www.nba.fi/en/museums

All - a worthwhile day trip is the little town of Fiskars.
http://www.fiskarsvillage.fi/en/

In the area there's also a Bison Farm close to Karjalohja.

Please think about Järvenpää. Great eats and a frozen lake right next to the center.

You dont need a car for this
Visit Suomenlinna sea fortressYou can easily spend a whole day on the island and the fortress and surroundings are great fun to explore for kids
There is even a submarine