We were asked:
What a lovely problem/challenge to have!
I guess the first thing to do is to gear up some expectations for yourselves beforehand. Basically, it’s unlikely that there will be absolute silence as you make your vows: the key is to get a generic blur of noise rather than something really distracting. Even then, if a kid does say something loud and inappropriate, then the comedy will give everyone something to remember your wedding by, and people will smile at the memory.
In terms of including them in the service
This isn’t a theological question so much as a practical one. Kids are good at carrying things, and generally like doing so, so having them carry flowers or even the ring can be lovely. If one of the older ones is up to doing a reading, that would be very special. But there’s no ‘set’ role for them.
One suggestion is that you allot one or more adults (who the children know) to be in charge of them during the service. Those adults (who shouldn’t be you or your fiancee and probably not your parents) will know that their job is to keep their allotted children entertained/ in a straight line in a bridal procession/ whatever. Sometimes a brother-in-law or sister-in-law comes up trumps for this kind of task.
Bring simple but quiet things for them to do during the service. It doesn’t have to be big: just a few pens and paper for them to do some colouring should work well, or soft toys for some. If the children are in the bridal procession, then leave the pens and paper on their chair/pew for when they get there. Don’t bring loud toys, though: a surprisingly easy mistake to make, but one that can lead to trouble.
In the worst case scenario
And the actual key bits of the wedding where you are looking for it to be as quiet as possible aren’t that long: so hopefully it should be okay. In the worst case scenario e.g. a baby who’s really howling, you’ll just have to hope the mother/ father is sensible and takes them just outside for a bit. In some churches, they have a side room that can act as a kind of a creche and the sound can be piped in, but it sounds like you want your children to be in the Church itself, so that wouldn’t work. And I’m really glad you’ve invited the children to the service. It’ll be special that they are there.