As @LangLangC found, there is a more recent study also reported by Nationwide Children’s Hospital:
Study results showed from January 2000 through June 2017 there were 2,968 ingestions of marijuana by children younger than six years old reported to U.S. poison centers. The majority (72.4%) of exposures were in children younger than three years old. More than half of all pediatric patients received some form of hospital-based care, of which 7.5% required critical care. Symptoms in patients ranged widely, from drowsiness and confusion to seizures and coma, and required medical treatments including hydration therapy, sedation and intubation.
This would likely be what NBC was reporting as the NBC article dates to June 7, 2019 and the Nationwide Children’s Hospital article dates to June 6, 2019. The journal article described is here from Pediatric Emergency Care. Quoting from the paper (emphasis added):
Pediatric patients experienced a wide range of symptoms from drowsiness and confusion, to seizures and coma.
Henry Spiller also co-authored a 2015 paper that reported on the symptoms of marijuana exposure in children under 6 within the US. The Nationwide Children’s Hospital also reported on this study (emphasis added):
The study, published online today in Clinical Pediatrics, found that the rate of marijuana exposure among children 5 years of age and younger rose 147.5 percent from 2006 through 2013 across the United States. The rate increased almost 610 percent during the same period in states that legalized marijuana for medical use before 2000.
...
The study findings showed that most exposures resulted in only minor clinical effects, but some children experienced coma, decreased breathing, or seizures. The main psychoactive ingredient of marijuana, THC, can be especially high in marijuana food products, and that may have contributed to some of the observed severe effects. More than 18 percent of children who were exposed were hospitalized. These hospital admissions were likely due not only to the clinical effects, but also the need to investigate the circumstances that lead to the exposure in the home.
The press release says some children experienced seizures, and not most or all. The study is available here.
@LangLangC noted:
The study lists 4 multi-seizures, 6 single seizures in 13 years for 1969 unintentional exposures (ingestion of large amounts) translated to 0.5% percent combined.
Thus, though not common, seizures have been reported as a symptom of pediatric exposure to marijuana.
Can ingested marijuana cause seizures, specifically in children?
Yes, ingested marijuana can sometimes cause seizures in children. This is an uncommon symptom of marijuana exposure in children.
This said, one of the active compounds in marijuana, cannabidiol, can have positive effects too. In fact, the FDA recently approved a cannabidiol oral solution for the treatment of seizures in "two rare and severe forms of epilepsy." From the packaging insert, this drug is approved for children as young as 2 years old. The results of the clinical trials are an interesting read and are available on page 16 of the insert. Thus, marijuana may also have a preventative effect on seizures. Marijuana is more widely known for causing suicidal thoughts. “The high prevalence of adolescents consuming cannabis generates a large number of young people who could develop depression and suicidality attributable to cannabis.”
In the comments, there is some discussion about Henry Spiller's expertise (or lack of) as he is the sole author mentioned in the Nationwide Children’s Hospital press releases. I would like to point out that as director of an accredited Poison Control Center he may have some expertise the other co-authors of the 2019 paper (all physicians) may not have had, and thus, invited to contribute. It would also be helpful to consider the credentials of the other co-authors before making conclusions about the validity of the paper.
