I'm not really sure how it all works, just what my accountant has told me. She's a semi retired accountant after I believe she said 20-ish years, taught accounting and now just does it on the side for around I think 300 clients. She considers this part time lol. I've just taken her word for it that 50% was the correct way. Mickyc's accountant does it this way too so again, just assumed it was right. I'm only a family of 2 and I'm sure it probably does work out to be fairly close to 4 kids but who knows

I haven't been audited but have every single receipt for record. Like you said, maybe the little bit of difference isn't a big deal in the long run and that's why it's allowable?