Sure, but set them up for success:
Pre-measure cereal into a container they can pour from neatly (i.e. probably not the box)
Pre-pour milk into a smaller container (that stays in the fridge overnight, duh)
(We actually did both these things when our oldest was about 5, because he'd wake up a 6 am and be ready for breakfast. Syrup pitchers -- like the kinds you get in diners -- are available at thrift stores, and are the perfect size to hold milk for one bowl of cereal. And if they spill, it's 1/2 to 3/4 cup all over the place, not an entire bottle of milk. Ditto the cereal in a small-ish container.)
Have the kid(s) practice pouring into a bowl while you're watching, so you can see what is and isn't going to work, and fix the latter.
Can the kids get their clothes out of the dresser without making a mess? Can they choose shirts without making a mess? My 8-year old niece has so much stuff in her drawers that if she's looking for a particular shirt there's no way she can find it and get it out without making an enormous mess. I'm a big fan of Marie Kondo-style folding and loosely packed drawers.
In general, encourage your kids to do the things they can do (and you can check Montessori sites for what you might expect children of various ages to be able to handle), but it will take a bit of training and some attention from you at the start, to make sure they're set up for success! (Also, take note -- if you're patient about teaching what you expect and how to get there, 5 years old is definitely old enough to do some cleaning with you.)
Good luck!