Agree with the poster who says small children/babies are physically demanding but preteen/teenagers are emotionally demanding.
I have 2 Dc's, my DD (11) is going through puberty, and all the emotional rollercoaster that goes with it, some days it's emotionally draining , and yes I know we're only just starting on that road.
My Ds (7) was hard work as a baby, always ill, colic, ezcema , didn't sleep well until 18 months etc. That was more physically demanding, yes it was emotional but it didn't involve the baby answering back, attitudes and all things hormonal like puberty does.
I was speaking to my Mum yesterday saying that we've had a tough week with DD's behaviour . My Mum says that you just have to 'ride on through it' that whatever you do you can't really win, just focus on the really important things, like keeping them safe and giving good advice, and hopefully at the end of it you'll get that beautiful, lovely wonderful child/adult back that you gave birth to.