The culprit here is not the bride and groom, it is the high cost of weddings. If you are having a buffet in the village hall, you can afford to invite more people, but if the venue for your reception charges like a wounded bull for each person you invite, including children, then you have to make some hard decisions. And venues will have maximum capacities too, whereas with the village hall option, you could pack in as many people as you wanted.
Dh and I had a village hall reception, back in the early 90s - because with our budget, that was the way we could afford to invite all the people we wanted there. The local pub did the catering, and because MIL was on the Parish Council, we got a hefty discount on the hall rental. And it was a lovely day - perfect for us - and we did invite some children, though only a couple of the people attending actually had children, so it wasn't a major issue.
Ds1 got married last year, and he and his dw had their wedding at a specific wedding venue, so they had to look at their budget, and cut their coat to fit their cloth, so it was a smaller wedding, and there were no children there apart from the bridesmaids.
Both weddings were wonderful family occasions - very different, but each perfect in their way.