“If a kohen should be served first at meals, does that mean that a host should serve the children, who are also kohanim, before her adult guests (who are not kohanim)? Wouldn’t that be outright disrespectful??”
Yes, indeed I would consider that extremely disrespectful and there are many poskim (such as the Magen Avraham) that say Kohanim do not have the same yichus they used to and are no longer entitled to these kibudim. I have asked Rab Forst shlita and he said that Kohanim today should not take priority in the meal or tzedaka. go to http://www.oraltorah.org to hear a great shiur from YU Rabbi Michael Taubes on this.
Be careful not to impose your chumras on other people!