"But Mummy I have to go NOW!"

Yes, one of those a mother ignores at her peril.
This one came in the library just as  "mummy" was about to get a pile of picture books checked out. 
She looked at me. I nodded. She rushed her not quite four year old off and left me with the not quite two year old in his stroller. 
He was jigging around and trying to get out so I played a sort of "peek-a-boo" with him. He grinned, wriggled some more and made it obvious he wanted me to do it some more. When his mother returned a couple of minutes later he was laughing.
She thanked me.
The older child, now quite calm, borrowed his books and they left. I collected the book I had on inter-library loan and went out as well. They were still getting into their car. 
The mother stopped what she was doing as I passed them and I said,
       "He's growing up fast."
       "He's not talking yet," she told me. She looked worried and I know she is worried about all sorts of things.
       "He's doing well," I told her and meant it, "Just keep on talking to him and reading books to him."
       "Oh, he loves books. He can point to a lot of pictures now."
We chatted for a moment longer and then, feeling some more spots of rain I pedalled off.
Her younger child, the one I was playing with for a moment, will be a worry in many ways. He has Down Syndrome and he will learn more slowly. There will almost certainly be health issues and other concerns. 
But he is a cheerful, outgoing little boy and he is incredibly fortunate because he has been fostered into a family which loves books. They are teaching him to love books too. He's going to be all right in the end.