Why do you think you would like this particular type of job? A) The job listing made the position sound fun. B) I love working with children and even developed some games to enhance their learning. c) I have children; I thought I might as well get paid for what I already do at home for free. d) I like kids and it fit within the hours I have available to work.

I think B) is the best answer.

A) makes you sound like you don't have a professional interest in the company, and they might assume that you aren't serious about the interview.

B) shows the reason why you selected the job option, and gives an example of what you've done before that displays your passion for the job.

C) doesn't really need an explanation. If anyone says that, the only results they should expect from that interview is the interviewer possibly socking them in the jaw. (Although, if you need an actual explanation, it's highly unprofessional, uncourteous, and a very good reason to get kicked out of a window.)

D) isn't completely awful, but it's a bit shallow.