As has been pointed out, there is a syntactic ambiguity in the portion of the sentence following “there’s”. It is not, however, a “misplaced modifier”. In this sentence, “coming out” is not a modifier, and it is certainly not misplaced. It is a gerund verb phrase in its canonical location, right after its subject.
Your intended reading might be bracketed like this:
[a movie about The Cat in the Hat] [coming out]
Here, there is a noun phrase “a movie about The Cat in the Hat”, consisting of a smaller noun phrase “a movie” and a prepositional phrase “about The Cat in the Hat”. This whole noun phrase serves as the subject of the gerund verb phrase “coming out”. Everything comes together to form one big gerund verb phrase, complete with subject.
The unintended reading that you noticed might be bracketed like this:
[a movie] [about The Cat in the Hat coming out]
Here, there is a noun phrase “a movie” followed by a prepositional phrase. The object of the preposition is the gerund verb phrase “The Cat in the Hat coming out”. Everything comes together to form one big noun phrase.
A number of facts about English conspire to create this ambiguity between the two readings. Off the top of my head:
-the “there is” existential construction can take as its object either a noun phrase or a subject + gerund verb phrase
-a prepositional phrase follows rather than precedes the noun phrase it modifies
-a preposition can take as its object either a noun phrase or a subject + gerund verb phrase
-a subject precedes rather than follows its verb
If any one of these parameters were different, as some (maybe all) are in various other languages, the ambiguity would be gone.
But just because a sentence is ambiguous doesn’t mean it has an “error”. In this case, following the standard rules of English syntax happened to result in an ambiguity. This happens all the time, we just don’t notice it because we’re good at using contextual and even statistical clues to disambiguate, without even being aware of it.
Stylistically, on the other hand, it is a good idea to avoid ambiguity, and I think your rephrasing, “a movie coming out about The Cat in the Hat”, with its postponed prepositional phrase, is a good way of clearing up the meaning.