I wanted to mention that red food coloring used to make my son very emotional.
Also, Emotional Freedom Technique (EFT) is great for this type of thing. It is a tapping technique on acupuncture points that is sooo easy to teach yourself. If you go to http://www.eftuniverse.com/ , click on Learn EFT, and then click on Go to the Free EFT Get Started Package you can provide you email to get the very short and very easy to understand EFT guide.
Anyway, if you practice it on kids it can calm them down. Here is the index of children's cases http://www.eftuniverse.com/index.php?option=com_content&a... . Here is a nighttime procedure that is very helpful with kids http://www.eftuniverse.com/index.php?option=com_content&a... . A good setup phrase for him might be "Even though I cry sometimes, I am a great kid" then the short phrases for tapping might be cry too much, cry sometimes, cry at school, etc., etc. Good luck.