Visual aids are simply devices or tools used to make difficult things to be simple and for ease of understanding of message being passed.
The main Purpose of visual aids is to speed comprehension and listener's interest, improve audience memory recall of content, decrease presentation time and others. It help keep everyone on the same page of understanding concepts with lots of working parts. The types of visual aids includes objects, models, and handouts, Flip charts & posters, marker boards & chalkboards e.t.c
We are given with a statement given above. The answer is D since there is no erratum involved in the sentence. Children is already plural hence placed after n. Monkey bars and swings are not in the state of owning something so there should not be any apostrophe placed.