grammatical number - "These are my children who want me to..." or "It's my children who want me to..."? And why?

Which of the following two lines is correct?

• These are my children who want me to learn cooking.


• It's my children who want me to learn cooking.

I am not very familiar with the codified rules of grammar, but based on my reading experience, I am pretty sure the second line is correct. But then, I don't know why it is so. Isn't "children" plural?