Much that is often wrong with childhood behavior is a result of the lack of self-discipline in parents - parents who do not read and obey the Book of Proverbs. There is also an obvious link between so-called ADHD and constant video games, and visual stimulation (all designed to hold the attention, so that normal life becomes boring in comparison).
On the other hand, diet no doubt plays a great part in producing physical temptations. Gluten, nitrates, MSG, etc., can cause nervous, anxious, even maddening temptations to those sensitive to them.
Cane sugar and high fructose corn syrup are really "drugs." The Bible teaches to eat a little honey. But cane sugar is not honey, and it is found in almost everything, and it creates a high, where children can become out of control. And how many children are given caffeine in sodas, chocolate, etc.? There are other sweets that are Biblical and healthy, that do not cause as great a sugar-high.
But there is a major link between BPA in plastics, etc., and hyper-activity, and this is missed by many parents! Notice:
"Bisphenols used in polycarbonate plastic containers and linings of aluminum cans have been associated with obesity and attention-deficit/hyperactivity disorder..."
(American Academy of Pediatrics, July 23, 2018)
"Children who had BPA concentrations at or above the median of the sample had higher prevalence of meeting criteria for ADHD...than those with BPA concentrations below the median...Higher urinary BPA concentrations were associated with ADHD...for BPA concentrations above vs. below the median…We found evidence that higher urinary BPA concentrations were associated with ADHD in U.S. children…"
(Environ Res. 2016 Oct;150:112-8. doi: 10.1016/j.envres.2016.05.040. Epub 2016 Jun 6.; "Association of Bisphenol A exposure and Attention-Deficit/Hyperactivity Disorder in a national sample of U.S. children")
"Bisphenol A (BPA) is an endocrine-disrupting chemical. Studies have shown that the exposure to BPA is associated with attention-deficit/hyperactivity disorder (ADHD) during adolescent development…Our findings provide direct evidence that childhood BPA exposure may be related to ADHD and 8-OHdG concentrations for children…”
(Environ Pollut. 2018 Apr;235:141-149. doi: 10.1016/j.envpol.2017.12.056. Epub 2017 Dec 23.; "Relationship between bisphenol A exposure and attention-deficit/ hyperactivity disorder: A case-control study for primary school children in Guangzhou, China")