Judge Matthew Deery said the upset of their parents, who understood the dangers associated with such wounds, had not been mirrored in the children.
The judge said Lee Cox, aged 4, and Helen Brown, aged 3, had been taken to their doctors to get injections, which was not uncommon for children. Fears an adult might have of developing bloodborne diseases could not be associated with them.
Therese Cox, mother of Lee, and Ann Hand, mother of Helen, both of Killinarden, Tallaght, Dublin, had sued South Dublin County Council on behalf of their children.
The Circuit Civil Court heard that the two children, now aged 8 and 7 respectively, had been playing on Oct 17, 2009 in the nearby Killinarden Park when they found in the region of 20 used and discarded syringes, some still with needles attached and containing traces of blood.
Ms Cox and Ms Hand told the court that when they had been alerted by older children of the find they rushed immediately to the park. They noticed Lee had grazed the palm of his right hand with a syringe while Helen had pierced the skin of her right thumb.
Barrister John Doherty, counsel for the local authority, said that the park was open 24/7 to members of the public, some of whom used it as a dumping ground for rubbish.
Mr Doherty said that while there was an antisocial problem and use of drugs in the park, the county council, in association with gardaí, had done everything in their power to deal with rubbish clearance and drugs abuse.
He said the council could not in any way be held to have been negligent in its duty of care to the public using the park which was surrounded by houses.
Judge Deery, dismissing the claims, added that the council had installed CCTV and employed specialist teams of staff with a tractor and trailer and a JCB to keep rubbish cleared from the park. The court could not say the local authority had acted with reckless disregard of the children.
He said council staff were filling two large skips of rubbish and taking it from the park each week. The council was making reasonable, if not entirely satisfactory efforts, to deal with the problem.