Hey Herolinda!
No problems posting in English, we got good education here, just like Germany i guess
Anyway i somewhat agree with Cat, Amsterdam is a fun, but somewhat weird place to visit for tourists. Most come for the coffeeshops and since you have your kids and wife with you, that's not the prupose on your visit there.
However, Anne Frank Museaum, Leidsche Plein and "de Grachten" are nice to visit!
I would visit Utrecht over Maastricht, it's located more central Netherlands. "De oude gracht" has a nice shopping centre and alot of nice cafe's you can do a cola with your kids.
Maastricht is nice tho, but a 2-3hour ride from Amsterdam.
If you want to visit the beach and a nice City, Den Haag .. The Hague, is a nice place to visit. Maybe visit a family musical there, alot present in The Hague.
Conclusion: visit Utrecht and The Hague.
Good luck,maybe when you are in Holland, we might bump into eachother