I am constantly doing things as I go along. I don't go up or down the stairs without taking something with me at the same time. I rinse baths out straightaway, I clean grill pans straight after use, the change bag/buggy/car get cleared out same day. I never ever go to bed without the kitchen and lounge being neat as a pin. Even when I am K.n.a.c.k.e.r.e.d. 
I make sure I have very good storage and I have decluttered the whole house from top to bottom to the nth degree. (this takes ages but once it's done it's done). Anything that starts looking suspiciously like a pile is eradicated asap. Anything that is out of place either doesn't belong in the home or you make a place for it. Coats get hung up, shoes go in the big chest, gloves and hats are in a drawer, toys are in toyboxes, dvds are in cupboards, everything has a place. My only bugbear is laundry because it is suddenly there in a pile needing ironing and that can be hard to fit in.
I didn't used to be so tidy, in fact I was pretty messy. Extremely messy. I used to wonder how "other people" did it. I then had a realisation that the ONLY way to be permanently organised was to a) get a cleaner and a housekeeper or b) be permanently busy doing stuff in the house. If you want to be tidy and organised, and you don't pay for extra help, you have to accept that there is less sitting-down time and more on-your-feet-and-doing time, especially in the evenings. It's either that or accept that your house/life is messy and disorganised and learn to love it. There IS no middle ground or magic answer. (I used to think there was but there isn't).
You won't convert your DH to suddenly helping (although you can try giving specific tasks). My DH doesn't lift a finger unless I ask him. So he will ignore taking the bin out for weeks but if I ask him he'll do it. However he works hard, he's a good DH, he does the garden and the DIY so I accept it as part of the balance.
Your older DC need to have it ingrained in them to tidy after themselves. Dishes go in the dishwasher, they shouldn't be allowed to leave their room messy for more than a day (but make sure you have given them adequate storage for everything). They should be able to help with basic tasks to like a five-min tidy up before bedtime. No way should they be allowed to leave stuff out in general/grown up areas. 9yo can probably hoover. As for the baby, try getting some wicker/woven basket things for the lounge/hallway so you can put their stuff together in one place, or at least be able to tidy muslins, toys etc together at the end of the day. Don't let baby clothes/nappies/paraphernalia get all over the house. It's either in the baby's room/cot area (in proper storage) or it's in a wicker basket in the lounge/hallway.