Whenever my budgie Blueberry gets a chance, he will try and sneak in a couple of poops to eat when I am not looking...or so he thinks. It turns out I just need to use a stern voice and he stops and flies off to his perch.
It turns into a habit very quickly and it is best to discourage them from doing so. Generally, it's a good idea to provide an environment where the poop falls through a grate and they can't access it. Sometimes they see a poop stuck to the cage and peck at it because it's something to do.
Provide them with a good quality mineral or iodine block. I generally find that poop eating is correlated to a lack of iodine. Males seem to be more into poop eating and lacking nutrients, especially iodine, and probably because they are more active and hormonal, so they tend to eat and burn through their calories quicker.
All seed diets do not provide all the nutrients your budgie needs so start getting them into a seed/pellet mix with a moderate amount of pellets to a regular or half amount of seed like Harrison's (SuperFine High Potency first 6 months and then Adult SuperFine) or Roudybush (Crumble). Start slow at first by adding a little bit of pellet to their seed to get them use to it.
Follow the suggestions from FaeryBee and StarlingWings and browse around the sight, do a search specific to topics of interest you may have, and you will find a plethora of information to get you on the right track with your keets