A 12-year-old boy sustained a broken arm during an assault by two other youths in the vicinity of Railway Square on Sunday afternoon.
The attack occurred around 3.45pm and the boy was brought to Waterford Regional Hospital for treatment.
Two youths were later arrested and are helping gardai with their enquiries.
Meanwhile gardai are warning motorists to be vigilant after a spate of car break-ins over the weekend.
Despite constant warnings by gardai, people are continuing to leave valuables items in cars, which make their vehicle a likely target for vandalism. Amongst the items regularly stolen from cars in Waterford are handbags and wallets, laptops, mobile phones and satellite navigation systems.