Some children had to sit against doors in the section between carriages on their journey between Mallow and Dublin yesterday.
Angry parents said it was an extremely dangerous situation and said they wanted to highlight serious safety concerns.
One group of parents also said they will demand refunds after forking out almost €200 to pre-book seats that couldn’t be used.
It appears as if passengers who had not pre-booked had boarded the train before them and sat in their seats.
The fiasco started when dozens of young GAA players from clubs across the county boarded the 8.30am Cork to Mallow train for what was supposed to be one of the most exciting days of their lives.
They were among several clubs from Munster who got a once-in-a-lifetime chance to play at GAA headquarters as part of the annual Croke Park Activity Day.
The train originated in Kerry. Passengers changed train at Mallow for the onward journey to Heuston.
The Skibbereen-based O’Donovan Rossa club’s under-12 football group had reservations for the trip from Mallow to Heuston.
The club’s assistant treasurer Anne Crowley said she booked tickets for 32 people — 20 youngsters and 12 parents to accompany them.
“We spent two hours booking the seats online a few weeks ago. We spent €91 for family tickets, including two adults and up to four children, and got a good deal,” she said.
“Then we spent an extra €6 per person, or €192 in total, to pre-book designated seats. We got confirmation and everything.”
But when they boarded the train at Mallow, they were shocked to discover the carriage on their booking reference wasn’t part of the train. All the remaining seats were full.
One of the club’s officials met a man accompanying another team who had a pre-booked ticket for the same seat but a third person was sitting in it.
Club PRO Garry Minihane said people were “jam-packed like sardines”.
“It was obvious the train was overbooked — by as much as 200 people,” he said.
Children sat on the floor in other parts of the train. “It should not happen in this day and age,” he said.
Mr Minihane, who is a paramedic, said if the train was involved in an accident even at just 10 miles per hour, there could have been serious injuries.
“We want to highlight this as a safety issue and to stress how dangerous it was to have kids and adults standing in the train,” he said.
The situation worsened when the train reached Thurles.
A woman in her 70s had to sit on a bag, and a distressed mother taking a sick child to hospital in Dublin had to stand, Mr Minihane said.
Irish Rail’s customer charter states that if they fail to honour a seat reservation, and no other seat of similar standard on the same service is available, it will refund the fare of the single journey in travel vouchers.
A company spokesman said it had not received an official complaint yet.
“We would like to hear from anyone on the train who had a problem, and we will deal with it,” he said.
“We will apologise for any inconvenience caused and deal with the issues.”
He said the situation highlights how important it is to pre-book seats online to ensure there is no overcrowding, especially at weekends and during the busy summer season.
Irish Rail has officials on trains to ensure people who pre-book seats get to sit in them, even if they are already occupied by somebody else.