Actually Spring, many many children in various situations (I am not saying this is the case here) do go off with peace and hope with other adults they know to be safe - IE patently obviously 'safe', as in the Police in uniform who collected the children from X location and then to the emergency foster home that SS have placed them with.
The only thing vis the above is that, by definition, given the privacy of the children and the nature of proceedings, we don't often hear about it. One (rare) example where we do know of it would be Shannon Matthews who made it very very clear that she did not want to go home with her Mother.
It's awful and I suspect most of us would prefer to think it doesn't happen as just how horrific must a child's life experiences be that that is the choice they articulate?
But just because most of us would prefer it would never ever happen that a child would feel safer out of his/her home than within it, just because most of us have no experience of it and only the 'normal' maternal experience of knowing our children would be distraught and panicked to be forced away from us, does not mean it doesn't happen (again, I will reiterate I am not referring directly to OP here, more the broader issues & feelings that something like this raises for a lot of us).
My understanding of foster carers (although I'm happy to be corrected) is that the kind who are able to respond to emergency removal cases and very sudden emergency placement are the most experienced, both per se have much experience and also have experience of dealing with disorientated and still reeling youngsters in that very sudden kind of placement.
My primary concern vis this specific matter is that the children concerned are okay and are hopefully right now out playing in a park somewhere with some very skilled, and very caring, foster parents 