I do think it is a lot harder when they're younger, but gets so much easier as they get older.
My DDs are almost 10 & 7 now. They're perfectly capable of getting up, getting their own breakfast, making me a cup of tea and so on. The actual care for them is very little now, as they are generally quite self sufficient. I would say DD2 adds to the washing, but most other things she doesn't particularly. She gets her own breakfast, dresses herself, washes herself (supervised ESP on hair wash days), yes we cook for her, but we'd be cooking anyway and her hobbies all fit inside the hours of DD1s hobbies. So there's very little 'cost' to her.
However, the benefit is that she entertains DD1. They go off to the park together, and won't come back until lunch. When they're together, they don't need me to entertain them. This school holiday, I've barely seen them as they've been off out and about together.
Yes, they argue from time to time, but they play together more.
I would say now that the benefits outweigh the costs ATM.