As a father of not one but TWO sets of twins 
under the age of ten it is important to find something that we all can enjoy and accomplish when we are in the great out of doors. We as a family of 6 make the trip to Yosemite National Park every year. We have whittled them down to a top three must do events each time we head to camp in the valley.
Go Ride a Bike
There are over 12 miles of paved bike trails in the valley and many more dirt trails. It is always an awe inspiring day to ride around the valley and take in just how small you are compared to all the granite walls around you. 
The good news here is for those with little kids there are plenty of places to stop and rest. You you can get snacks along the way at the various cafes and shops.
You can bring your own bikes or rentals are available for rental near Curry Village,
Float down the River.
This is one of my personal favorites! The Merced River weaves its way through Though Yosemite Valley. It moves slow enough to enjoy the sweeping views of Half Dome and nature around you but quick enough in spots that the small kids get a little excitement. There is only one place where you are allowed to “put in” your boats but the 2-3 hour trip down stream is so worth it.
Raft rentals are also available in Curry Village and there has to be enough water in the river to be open. If you bring your own raft don’t forget the life vests for you and the kids as it is a rule of the park.
Hike to the Top of the world!!!
The hike to the top of the Sentential Dome seems like it is a little known trail. Perhaps, because it is a short hike or maybe because there is a car trip out of the valley involved. But this is a great family hike! Last year our four year old set of twins made the hike easily. It is a 2 mile hike that takes you to the second highest point in the park. You are higher than Glacier Point and Half Dome. One Hiker explained to me “it is the same views of the valley without having to hike for 13 hours like the hike to Half Dome.”
The trail head parking is limited but I think that is the only down side of this hike. For those who are looking for a hike with grand views and an easy to moderate climb this is it.
Go have a family adventure!
The Story of Elmer in Yosemite 