I really want to go back to New York but I always said I would wait untill my daughter is 7 or 8.
Since that will take another 5 years and I really mis the city I was wondering: Should I visit New York with a 3-year old? Are there things to do for her? Offcourse having a small kid limits the options but what are the possibilities?
Is it recommended or not.

There are a lot of things that you can do with small children in the city. I would skip a lot of the touristy, crowded areas like Times Square because it's hard to move around effectively with a stroller.

Ideas:
The Central Park Zoo, Museum Family Days, Carousels in Central Park/Bryant Park, Boat trip around the island, there are lots of new kid-friendly parks on the west side of Manhattan in Riverside Park, Bronx Zoo, and so much more.

Time Out New York has lots of options for kid-friendly events in NYC.

Thank you very much for the information.

Keeping your reply in mind we are planning a new visit to New York for next year!