Killies are not particular more difficult to feed than other fish. Many of them will take crisps and flake food if they are trained to do so. But as with all fish - the more varied menu you give them, the more happy you and they will be.
The killi hobby is a lot about breeding fish. Following you will also have to deliver a menu that vary a lot in size so you have the right sized food for the current age and size of your fish.
When dealing with annuals you must be prepared that many of these are growing VERY fast and some of them are ready to spawn in only 6-8 weeks. You can imagine that this grow rate needs something quite special.
Most killi keepers use different kinds of live foods. There are many types of live food and some of them are mentioned here below. Some cultures you can start yourself and other live foods requires buying a starting culture. Cultures can be bought from the same sources as the fish, but also your local Killi Association could be helpful with some kind of starting culture. Click on the links below to find more info about different good killi food.

When you feed your fry, young or adult fish be always careful not to over feed. Uneaten food left on the bottom or in the gravel will pollute the water. Feed your fish well but remember to look how much they actually eat, and also remember to make your water changes. Many killi keepers have a snail or 2 in their tanks working as a bottom cleaners. But still frequent water changes and bottom cleaning is necessary and important.