I don't know.
I think a lot depends on the child and their personality.
My 3 were quite easy babies, all slept through by 6 months. I bf and found it easy just to go anywhere, food on tap and so on. Pretty normal toddlers, but all in bed asleep by 7:30.
When dc1 was 7 he was going through a very hard patch, very angry and mouthing off to me, doing the opposite of what he was told, running off and so on. At the same time dc3 was a toddler. I remember thinking that toddler tantrums are a piece of cake compared to 7 yo tantrums.
So I think that the early years are (or can be) much harder in terms of physical tiredness, and it can be very relentless if you have no support. Once they are older, especially when they are at school, there are more breaks and it isn't so physical, but they go to bed later, so your down time starts later (mine now isn't till 10 pm) and it is emotionally and mentally much harder.
Then again my 11 yo is so funny and good to be around, (when he isn't flouncing) that I really enjoy his company (most of the time)
I did find that once my toddlers could chat to me they were much much easier