A confession (or 3) and a question

Confession:  After doing a good workout on Wii Fit this morning, I totally came upstairs and ate chocolate cereal and potato chips for breakfast.  But I washed it down with green tea and chlorella, so I feel I maybe broke even.

Confession:  We bought several new pencil sharpeners for Christmas, AND I found a few more we had been missing. We *still* can't find one when we need it.

Confession:  I'm messing with their schooling again. Does this ever end?

Confession:  I just gave away several twaddly DVDs and an obnoxious little piano (a favorite of my little kids) behind their backs.  And I'm happy about it too.  And maybe just a little bit guilty.

OK, now for the question. Just how much do you allow your older kids to "nag" younger kids towards proper behavior?  I often hear my older two say things like, "Hold that thing with two hands!" or "Don't climb on top of the couch," etc...   I wouldn't find that problematic, except that my younger three HATE HATE HATE to be told what to do, especially from their sisters.  So instead of the scene ending when the cherubic 5 year old says, "Oh Juliet, you are so right, whatever was I THINKING when I tried balancing my lunch on one hand,"   I hear, "Leah, hold that with two hands," and then a huge, loud, whiney freak-out coming from the kitchen.  Which is much MORE likely to result in her dropping the dish in question than if we had left her alone in the first place.

But that being said, I can't be everywhere all at once and wonder if I should train the youngers to accept general admonitions from the older crew.  Any thoughts?