This sounds like the perfect topic for me!
At present I have a nearly 8 week old, 2 year old and 3 1/2 year old...and another 4 kids, a nearly adult DD and my sweet little grandson who is 11 weeks living here.
I agree with a lot of what Tarli said...organisation is key.

Even though I have a lot of kids living here, my house is normally fairly tidy and clean. Everything has a home and everyone contributes to the running of the house, right down to my 3 year old that I make clean up after himself.
Riley (my 3 yo) used to love getting into things so I can sympathise...know you are not alone there, some kids just like making mess! His 'best' mess was when he got into a 2 kg bag flour...I found him laughing and throwing handfuls in the air, while stomping to make clouds of it fly up in the air!!

How I wish I had taken a piccy of that!
I agree with Tarli about getting them involved when you are doing the household chores...they love helping! It keeps them out of mischief and it's nice spending the time with them.
ATM with such a young baby my house is running around her routine so any meal preparation that needs doing is done in the morning while she has her long nap. I also do the majority of the washing then too, and clean up after the kids have gone to school. The kids have a routine, and it works well, the boys both have their naps at the same time and they all have a bedtime. (except Sierra)
I also don't expect that every day is going to run smoothly...we all have bad days as do the children...I had a few recently when Sierra (my baby) was sick and very cranky all day. I felt like crying too, but we got through and things are a lot better now.
And finally, I also agree with Tarli that being consistent is very important...they know that even if I am sitting down b/f Sierra that if they do something wrong I will deal with it straight away. I find that definite boundaries and consequences when they are breached really helps.