Q: How to help kids to overcome short temper (easy to get upset or be irritated) ?

1. Practice mindfulness. Regardless of the situation, you can always get them to attempt to count one to ten and to breathe for a few seconds. You may need to start counting aloud with them and get them to follow along to form the habit.
2. Engage them in activities that trains their patience. Eg. In doing puzzles, mandalas etc. For a start, pick a puzzle with a design that is of interest to them and of a level that they can complete without much difficulty such that they will attempt and experience the satisfaction of completing the puzzle. You can gradually increase the difficulty of the puzzle or game. 
3. Consistently enforce waiting for their turn. Eg. If they interrupt a conversation, make it a point to remind them to wait for their turn before speaking. Remind them to take turns to use a playground facility. 
4. Pick up a sport or arts or any hobby that encourages discipline and also provides an outlet for them to express their emotions or release stress. 
5. Be a good role model. Kids learn best from role modelling. If they see that you consistently manage unpleasant situations without losing your temper and in an even tone they will pick up the vibes from you.
6. Where possible,if they get irritated at a situation, help them see the bright side of the situation or work out alternatives together.