A&E departments faced a rise of more than 20% in the number of young children being injured by violence last year, figures have shown.
According to data supplied by hospitals, 3,402 children under the age of 10 were treated after violent incidents in England and Wales in 2010, compared with 2,814 in 2009.
Researchers said the rise in the number of children being hurt was "a real issue", despite an overall drop in the number of injuries.
Across the wider population, 37,000 fewer people were treated following violence in 2010 than in 2009, after an increase of 8% that year.
"The trend is going on the wrong track," Cardiff University professor Jonathan Shepherd said.
"The question is why, but it's hard to pin down," he said, adding that recent changes making it more difficult and expensive to take children into care "may be a factor".
"There may be children left in risky circumstances where they would have been taken into care before," he said.
The figures, which come before the publication of British Crime Survey statistics later this week, showed an estimated 313,033 people were treated following violence in 2010, 37,000 fewer than in 2009.
The figures from Cardiff University, which collected data from 59 emergency departments and minor injury units in England and Wales, also showed that men aged 18 to 30 were at the highest risk of being injured by violence.
Violence-related hospital visits were most frequent on Saturday and Sunday, and peaked between May and October, the figures showed.