Child tax credit for children born after April 2016?

[TigerMa]

Hi all,
This is possibly quite a daft question but I could not find the answer myself.
I have three children, the youngest is born after April 2016.
My oldest is turning 16 soon. If she decides to drop out of full time education, or when she finishes it at 18, are her sister and baby brother counted as children 1&2 (as per the two children restriction for tax credits) or not? Thanks

The date that the rules changed were April 2017, but if you currently only get tax credits for 2 children then when your eldest drops off the claim , your youngest can go on.

Was it 2017, I only know he doesn't qualify at the moment as he's born after the cut off date.
Thank you, that's good to know.