As a veteran from the last church I belonged to of doing coffee hour, I can kind of understand what the OP was saying. There are probably as many solutions as there are churches, and I think that the key will be tempering the young un behavior but not turning them off from church, which many kids quite honestly see as something their parents drag them to, rather than something they want to go to (ever wonder why when kids get older, they disappear? Nothing like some old biddy lecturing them on proper etiquette.
Based on my war wounds, couple of suggestions:
1)I like what someone else said, having food for the kids. If you can afford it, maybe have a seperate ministry from the coffee hour that would provide stuff for the younger kids (HS age kids , at least in the church I was in, were in the main service). Bagels and cream cheese, or fruit and yogurt, something along those lines, will help defray, as others said, the kid getting up early, probably missing breakfast, and then going to church. Plus if they are full from that, they won’t grab the snacks as much.
2)If you want to get older kids involved, have an older kid (late teens) who is attached to the coffee hour ministry, whose prime duty besides helping out will be to (gently) monitor the younger kids. Not perfect, but it might work better than an ‘adult’ lecturing them.
3)The head of religious education should be told by the minister/priest (whatever kind of church it is, ‘da boss’) to tell the kids to be careful with chowing down in coffee hour. More importantly, why not hold the younger kids until the service is done?
I tend to agree with others, that the way you do this is important. I know a lot of people who won’t go near a church, because as kids they were treated as an annoyance or worse (not just churches, there was a local UU place where the membership were these older, well off people, who treated kids as this thing to be shuffled off on the side and hidden away, because they I guess annoyed the adults…to the point that the kids were not let out until after coffee hour had finished, like putting them in jail…I hear that federation is withering away on the vine, not a big surprise). One of the things churches face these days is many of them are seriously graying, and one of the reasons is many young people don’t view church as an obligation they ‘have to do’ as an adult, and more than few have bad memories of the way they were treated, and won’t even think of setting foot in a church of any kind. I did outreach for a pretty liberal church to try and attrat memebrs, and some of the stories I heard about why young people in their 20’s and 30’s didn’t want to belong to a church were sad.