At first glance, Amsterdam is not a great family destination. Who wants to be taking the kids into a hash-smoking den, or traipsing around the Red Light District? Or to a country that permits children from age 12 to have "non-exploitative" sexual relationships? To boot, a legal political party, the Brotherly Love, Freedom, and Diversity Party (PNVD), openly advocates pedophilia and child pornography.
A second glance is likely to be more promising. This is a largish European capital of a country in which kids are relatively highly regarded. There's also plenty of wholesome stuff for them to do.
Let's see now: pedaling a rented bicycle around town, or a water-bike around the canals; riding trams, harbor ferries, and canal boats; visiting Artis Zoo, the Anne Frank House, and one of several children's farms; exploring the beach at Zandvoort; swimming in the IJsselmeer; working off steam at adventure parks. And lots more.
Some of the city's more expensive hotels offer kids' suites, and you might even find that a suite is cheaper than booking two rooms. Many hotels allow children up to a certain age to sleep free or for a reduced rate in their parent's room, and may provide an extra bed.
Arrange ahead of time for such necessities as a crib, bottle warmer, and car seat (in the Netherlands, small children are not allowed to ride in the front seat).