P.
Dress to shoes!! My 5 & 3 y/o boys help pick up toys and put them in the proper containers. They will pick up other things around the house and put them where they belong. I have an extra, small vacuum and a dustbuster that I give them to help. I give them specific areas. What's great about the 15 minute increments is it keeps them engaged. When the timer dings they know something else is coming. Sometimes I'll even ask them what we should do next. Give them one of those Mr. Clean Eraser sponges and tell them to clean any marks, spots etc. that they see on walls and baseboards.
Your older children should not need too much direction once they get going. Get your 5 and 2 year olds to work together. Have the 5 year old carry the laundry basket or something & have the younger one put stray items in there to be put away, perhaps by the older children.
Give the little ones dusters, they love them and things actually might get clean! Remember, you can't expect perfection, just fix it later.
Good luck!