AOG
"Who will pay their maternity fees, educate them, house them, pay their benefits or look after their medical needs in the meantime?"
'They' will - through their taxes and national insurance contribution.
The essential flaw in your question can be summarised thus:
"It's going to cost billions to educate children over the next ten years...what a waste of money".
You see how that statement doesn't make sense.
Sure, if the children of immigrants all left school and didn't work, or took their skills abroad, then the question would have legs.
But that simply isn't true.