It doesn't sound like the invitation is saying, "local guests can't bring kids, out-of-townies can." It would probably have said as much. Saying that children of people travelling a long way can be "accommodated" sounds more like they are trying to be mindful of how hard it is to get someone to watch over children for a few days, and maybe they're going to help out with finding babysitters or something else of the sort.
I read this as "no children at our wedding thanks, but if you're travelling a long way and that makes things difficult for you, let us know and we'll help sort things out." It really sounds like they're trying to be very hospitable.
It's their wedding. If they don't want kids, there's nothing wrong with that. If they're going the extra mile by trying to help out those for whom children make attending the wedding difficult, good on them for that.