From the looks of your profile you are VERY busy!!!
I am a SAHM of 5. My kid's are 18, 16, 11, 5, and 3. There is not a dull moment in my house from the time I wake up until I finally get the 5 and 3 year olds in bed at night. I am constantly doing laundry and and going to the grocery store.
The only way I can stay organized and also keep the house picked up (notice I didn't say cleaned up)is by keeping a family organizer. My favorite is Amy Knapp's Christain Family Organizer. You can get it from Walmart. It has a full monthly calander for each month and then separately list the week of month with a weekely menu and grocery planning list that you can tear out. It is my life saver. It also has inspirational quotes, and a place you can write out monthly projects that you want to get completed. I could go on and on about this planner.
Also, I assign the little chores, like trash emptying, playroom picking up, clorox wiping counter tops down, setting the table, clearing the table, putting laundry away and making their own bed's to my 5 and 3 year old. This is a wonderful age for this, because they actual like doing these chores, because it makes them feel as if they are helping you! Your 5 year old would probably love to give the 5 month old a bottle or entertain him/her while you are fixing supper or folding laundry.
I also always lay out the girls clothes for the next day the night before. I do this even if we aren't leaving the house the next morning. This makes it easy for them to quickly get themselves dressed. My 5yr old now likes to do her own hair and brush her teeth by herself. At first the hair do was not GREAT, but it was something that I could live with, but she is getting better every day.
Also you have to remember that they are little only once!!! So what if your house is messy or unorganized. As long as you are spending quality time with your children and they are nutured and fed with good family values, and christian morales you are doing a GREAT JOB! There will always be time later to have a spotless house.
I hope this helps.
W.