Is it possible to develop bipolar in childhood? Does the same diagnostic criteria for bipolar in adults apply for children?
Yes but it is referred to as Disruptive Mood Dysregulation Disorder in DSM 5 and is characterized by persistent irritability and frequent episodes of extreme, out-of-control behavior.
1$\begingroup$ This seems partially backed up in the Pediatric News article "When is it bipolar disorder and when is it DMDD?": "A new diagnosis called disruptive mood dysregulation disorder (DMDD) was introduced into the DSM-5 to describe these chronically irritable children and, in part, to reduce the number of children receiving a bipolar diagnosis." However, it makes no claim that it is always diagnosed as DMDD as you imply in this answer. -1 $\endgroup$– Steven Jeuris ♦Oct 5, 2018 at 9:36