Most parents, regardless of whether they worked or not, who found themselves without enough money to feed their children would probably cut back on all non essentials first, they would find ways of cutting their food shopping bill, they would cope, they may even go without food themselves to provide food for their children.
Let's not forget that many working people who are above the threshold for receiving gateway benefits to free school meals are already going without to provide food for their DC. The parents who chose to have DC3,4 and 5 should still be entitled to receive free school meals and healthy start vouchers for their DC.
I would imagine that most of the parents who this would affect would rather go to a food bank than wave their DC off into care, so it is unlikely that the care system would be overrun by children. Maybe some DC would end up in care, but the majority would not.
If 2 parents + 2 DC were supported, they would still receive over £250 a week after their rent and council tax had been paid to buy food. Imo, if they choose to stretch that money to feed 6 people every week, it can be done, but they would probably have to sacrifice everything except the bare essentials to be able to do this.
If a single parent + 2 DC were supported, they would still receive approxiametely £220 a week after their rent/council tax had been paid to buy food. If they choose to continue having DC whilst claiming out of work benefits, that is their prerogative.
When I see threads on here written by people who have children and only £50 a week to feed themselves and their DC and pay their essential bills sometimes less , I don't see those posters in that situation considering putting their DC into care. They cope. It is not easy by any stretch of the imagination, but if they can feed their DC and themselves for £50 a week, I should think a family can feed themselves on £220 a week.