belches, and burbs, and farts oh my

Lately I've been tutoring several boys in E.S.L. Of course teaching E.S.L is not limited to written or spoken English. I am also obligated to teach culture and in this case North American manners (what little I know of this subject)
The first lesson was for Woojin 1 (I teach two). He is a very cerebral cute 7 year old who likes to produce a special affect while reading out loud. He inhales as he reads the text and sometimes uses a Korean accent as a joke, since his spoken English is perfect. He also likes to find reasons to stand up and walk around. Pretty typical. So, when he had to burb several times and wanted to go to the bathroom each time, I told him the trip wasn't necessary. To simply say excuse me would suffice. "Belch..Excuse me. Blech...Excuse me" and then a smile and back to the reading.
That same day another student, Yule, who is just a year older but seemingly a foot taller, asks "What name this? (he bleches so loudly his teeth almost rattle) What name this?", he asks again. I'm trying not to laugh, but do anyway. "Sorry. I'm not supposed to laugh. That is a burp or a belch.", I tell him with as much authority as I can muster. "Bup, What the other word?" "Belch", I say with only a slight grin. "Beelch", he repeats thoughtfully. I'm so amused by the whole thing that I almost forget to pedogogize. "Usually, we say 'Excuse me' after we belch.", I add dutifully. "Usually?", he questions. "No, just..always...just always say excuse me and try to make it softer when you belch." "O.k."
The following day I'm back at Woojin 1's house. He's moved on from the oh so quaint belching to the deadly. That's right. He actually sat while reading about TRex and farted! "Excuse me.", he pipes with his little voice. "No, that's not an excuse me situation. You need to go to the bathroom for that.", I say, once again almost laughing." He looks hurt. "But you said.... Oh that was for the other thing. O.k." He starts to walk to the bathroom and says "But now I don't have to do it anymore."