What sort of mess are you talking about?
Messy kitchen and bathroom - dishes piled high, bin overflowing?
Bits of games, blocks, crayons underfoot?
School papers/drawings everywhere?
Boots, shoes, cardigans, jackets everywhere?
Cars/trucks/vehicles/dolls/doll stuff?
Books everywhere?
Writing on walls?
Spilled drinks on couches?
Food/crumbs/wrappers/empty pots or juice boxes everywhere?
You can make your 6 year old pick up his clothes form the floor. If he can poop in school without being naked then he can manage it at home too. Tell him he is a big boy now.
Make the DCs eat and drink only at the table if food and drink messes are an issue.
While I agree that tidying up is futile, if your children are completely inconsiderate mess generators, I would do a tidy up before lunch each day with the 1 yo strapped into his high chair. Get the 6 and 4 yos to help or no lunch. Be firm about help and also cheerful. Don't dwell on the massive mess or who made it. Remark on how nice and tidy the house is as you eat lunch and thank them for their help, so they will become aware of the difference between messy and tidy and feel good about how helpful they are. After lunch, make them help clearing up.
Warning - they will hate you for all of this but standing your ground will pay big dividends in the end.
Insist on a quiet time every afternoon (90 minutes should do it) for the 6 and 4 yos while the baby is napping so you can catch your breath and clean up your kitchen. They could watch tv or read. You could also have a cuppa.
In the quiet time you can spray and wipe the bathroom, clean kitchen surfaces, take out the bin bag, maybe mop a floor or wash a few windows. Let the 6 and 4 yos clean skirting boards with wet wipes.
Let the 6 and 4 yos help with laundry too. They should be able to contribute to about ten minutes of putting away their own clothes, finding matches for socks, figuring out whose underwear is whose.