Parents need to know that this movie has no objectionable material. They may need to explain a few references, like Mayor Ed Koch and the allusions to old movies.
Positive messages:The motley, multi-species Muppets could be seen as a nice metaphor for multicultural urban society getting along.
Overall, not a bad movie for children. A lot of good messages are present, but I would not rate this movie as child-friendly as, for example, the Winnie the Pooh series. Parents should be aware that Dabney Coleman's character smokes in the film. Also, one female muppet remarks to another that she will "not take off her clothes, even if it is 'artistic'." These items did not seem to faze my 8-year old, probably because they went over her head - but parents should be aware of their presence in the film.
I picked the 5 to 7 age range 'cause I don't think it's good for 2 yos but many 3s and all 4s will enjoy. You may have to explain what "Broadway" and a "musical" are and why Kermit doesn't remember his friends but it's good fun.