The doctors could not force them to either go on the trip or cancel it. All they could do was give them the information they had at the time and let them make up their minds, and since at best they said something like "we're going on holiday in a few days" why would anyone imagine they were actually going to live in a van for months? I'm sure that isn't the doctors idea of a "holiday". Chris also definitely said he told them that it didn't matter if an appointment came through, they would be able to drive home anyway. Imagine what they'd be saying if they'd been told not to go and then an appointment didn't come through till they would have been back?
No one could tell them exactly how long it would be before they got an appointment, if they ever spoke to someone at Sheffield Childrens Hospital at all then all they could do was give the average time frame at that time, which can vary depending on how many people get referred, cancellations, whether they manage to clear a backlog. They wouldn't have spoken to a doctor and there was no time for anyone to have looked at the individual case since they claimed to phone the hospital minutes after being referred.
This is their 5th child and they should be well aware of the danger they put Mila in by leaving her in her car seat for such long periods of time even without the hip issues. The advice has definitely not changed since I had my first 9 years ago.
I have wondered whether Esme's latest injury they have tried to cover it up because of how it would look bad on them. If they are already being watched because of Mila, then Esme has an accident needing an A&E trip involving a knife whilst living in a van, then a week or 2 later she needs medical care again for another accident for something that happened with the family, it doesn't look good. Of course it could be something that didn't need a hospital trip, or they could have gotten her checked out, or contacted 111 and they made the call on how to treat it.... but by keeping it quiet it makes it suspicious. I'm all for keeping medical information private but they haven't with anything else, and when it's an obvious injury that they show in the background it seems strange to not mention it at all, even if they didn't give details.
The children that they have been having just for views are going to need some actual care. Jace still has ongoing appointments for his eyes, and may also need an operation. They have older children who never go anywhere else, no school so are in the house constantly. They live somewhere that none of them know anyone, and they are not close to any friends or family anyway. Unfortunately Isabelle is going to be left with the others more and more, probably whilst Chris messes around with the van/windows/floors and Sarah can't give up her shopping trips but will have to leave Mila at home.