Final answer:
The sentence with the dangling modifier is: 'Playing with the children, it was obvious they had a good time.' This modifier incorrectly modifies 'it', which does not refer to the person playing with the children.
Step-by-step explanation:
A dangling modifier is a type of misplaced modifier where the modifier doesn't have a clear connection to the subject of the sentence. In this case, option A contains a dangling modifier. The phrase 'Playing with the children' doesn't have a clear subject it is modifying, which creates confusion. To fix the sentence, you could rephrase it as 'While playing with the children, it was obvious they had a good time.'