Late, with daughter slipping out and son coming in? It's a strain (7)
I believe the answer is:
overuse
'it's a strain' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for overuse that I've seen before include "Employ too often" , "Excessive employment" , "Excessive utilisation" , "Wear out" , "Employ too much" .)