How to play with children?

I have 1 child, of course there will be no problem if I only take care of 1 child, as soon as I take care of my child, I have to take care of my sister's child as well. I'm really confused because the 2 children have completely different personalities. each other and have to be very busy feeding and sleeping them. I don't know how mothers can look after multiple children at once without letting them cry. Do you have any tips for babysitting?