I've got two kids: 15 month old boy, 7 year old girl. With the boy, the toil is literally keeping him from killing himself. If you put him downstairs, he'll try to climb up the stairs. He'll climb on the couch and fall off the other side. He'll drop things in the toilet. He'll try to pull stuff off shelves. He'll climb up the chair onto the dining room table. He is not content to sit and eat. I gave him cornbread yesterday, and he insisted on eating with a fork. (Basically just crumbling up cornbread to go everwhere.) If you take the fork away from him he cries. He does this 16 hours a day non-stop. He doesn't nap, he doesn't watch TV, etc.
The girl has no internal monologue. She has to run every thought in her head by you. Most of them are pointless and incoherent, but you have to humor her. She will say "um..." just to keep warmed up for the next thing she might want to say. She requires constant attention and affirmation. She wants you to watch her do a cartwheel--identical the previous million cartwheels--and respond enthusiastically. She won't eat her vegetables. We have a rule that we eat vegetables before we eat the rest of the meal. Every meal becomes a bitter war of attrition where she fights to eat green beans as slowly as possible, hoping you will give up. (Between boy and girl, eating a meal peacefully is impossible.)
Meals--when I was single I once went three months eating a turkey sandwich every day for lunch. Your kids will not put up with this.
Getting them ready to go out is a huge effort. They have a million accessories (bottles, diapers, toys, etc.). They have no sense of urgency. You are trying to get to church on time while girl is starting a craft project.
They generate huge amounts of clutter. Markers, crayons, paper, toys, etc. Taking a hard line on toys is little help, because their school sends them home with piles of art, crafts projects, etc.
They are very rewarding. When they're sleepy and both snuggling on the couch, I hug them and think "I will never do anything better than this." My wife and I will look at the older one playing with the younger one and say: "this is the best part of life, it'll just go downhill from here." The only reason we don't have a third yet is accounting for private school tuition. At the same time, my wife and I relish going to work every Monday so we can deal with angry opposing counsel instead of picking up after the kids.