Amsterdam has become tourist overload, like Barcelona and Venice.
So be prepared for millions of tourists, especially at Easter time.
I think now it's 17 million per year with 850 K inhabitants.
For a 6-year-old go to Nemo - Science Museum, like a sunken ship to the left of Centraal Station - 10 minute walk over the bridge.
Or Artis, the zoo, it's great with a garden with Buddha, café with kids playground, animal farm and a lovely aquarium - Tram 9 I think from CS. Hey! He will even love those tram rides!
Just get all the info about public transport etc. before you go. I think "I Amsterdam dot com" will give you a few pointers. (OV public transport chip card etc, (Oyster?) gives you access to the whole country if uploaded (20 Euro), there's a train to the beach, takes half an hour.
DO NOT hire a bike! Locals drive like maniacs on their way to work etc. and WILL RUN YOU OVER not on purpose! those stoned LOL tourists not looking! while checking their mobile!!
And as with trams, cars, bikes, only cross on the zebra/green light crossing.
Oh yea, North Amsterdam is on the ferry behind CS, also great for a little boat trip across the harbour.... Again, another 20K bikes to dodge. :-) But you get to see barges, etc.
Have a great time! Amsterdam is amazing.