Photo: Paramount Pictures

Tiny children: placid and cuddly one minute, bonkers and terrorizing the cat the next. The theory behind toddlers’ bad behavior has long been that they’re acting up because they’re angry or frustrated and haven’t yet developed the self-control or language necessary to deal with that anger in a more civilized manner — hence the sibling-bopping and babysitter-biting.

But Audun Dahl, a child development researcher at the University of Santa Cruz, recently published a study — highlighted this week by Christian Jarrett at BPS Research Digest — that proposes an alternative explanation. Much of the time, toddlers act like tiny terrors for absolutely no good reason. Dahl observed about two dozen more children in their own homes at three separate times — when the child was 14 months, then 19 months, and then 2 years old — for two and a half hours at a time. About half of the time a child intentionally harmed someone — usually a parent, though siblings and pets were next in the line of fire — there appeared to be no provocation. In about 43 percent of the interactions Dahl observed, there did appear to be a reason for their bad behavior — an annoying baby sister, for example — and the rest of the time the action seemed more like an accident.

If frustration or anger doesn’t explain all instances of toddler jerkiness, Dahl offers that biting Mom’s finger or whomping a day-care pal on the head might be a misguided attempt at having fun. Although, here’s a question: Just because Dahl couldn’t observe anything that should be bothering the toddler, how do we know for sure that means the little guy or gal wasn’t frustrated about something? On the other hand, as Jarrett notes, this new study “chimes with past research in which mothers reported their toddlers mostly showed signs of pleasure when they caused upset to other people.”

The good news: This behavior seems to disappear over time, peaking at 18 months and becoming less common by 24 months. Until then, enjoy life with your tiny madman or -woman.