Not sure it's a wise decision in the current economic climate, but I understand why they want to.
Instead, they should insist parents keep their dc in check, and ask them to leave if they don't, rather than a blanket ban on all children, as ours were always well behaved, simply because we would not tolerate them misbehaving, especially out in public. They would have been taken home, and missed out on the treat.
Our children knew the rules, if they wanted to eat out, they had to behave. It really is that simple. It's just a shame that nowadays, many parents want a quiet life, and so let their children do what they like, rather than reprimanding them or having to go home and missing out on a meal.
We went to many country pubs for meals when our dc were young, you just need to teach them how to behave.
When they were very young their attention span was less, so once they'd finished eating one of us would take them out to the play area to let off steam, whilst the other finished eating. If needed, we swap/tagteam it so we could both finish our meal, without other diners being disturbed by restless dc.
We didn't use ipads or phones or anything like that to keep them amused. At the most, we would have some colouring pencils and a little colouring book to do as they got slightly older and more able to cope, alongside an increased attention span.
They were not allowed to stand on the chairs or run around the restaurant/pub, and if they had tried, we would have told them off, and if they did it again, we would have left and taken them home.
It drives me mad nowadays how a lot of parents allow their children to just misbehave and run around whilst people are trying to eat.
Family friendly should not mean children running riot, but that takes effort, and many parents can't be bothered.