Over 500 children have been waiting at least two years for their first assessment with a speech and language therapist.
A further 700 have been on the waiting list over 18 months.
Children often need speech and language therapy if they have communication issues or problems with chewing or swallowing.
According to new figures, released to Newstalk under the Freedom of Information Act, there are currently 16,466 children on the waiting list.
Some 3,685 children have been waiting over a year for an initial assessment – including 516 children who have been waiting at least two years.
Children’s Rights Alliance CEO Tanya Ward said the number of children waiting two years is a disgrace.
“It is a shocking figure and it is very serious because with speech and language, if you delay providing a child with an assessment, it essentially means you are also delaying them gaining access to therapy,” she said.
“That will have a big effect on them later in life. It will have a big effect on how they do in early years settings, how they do in primary school, how they do in secondary school and it will certainly mean they never reach their full potential.”
She said the children will face difficulties that could have been avoided if the system was functional.
“It will delay how they do in school and it will delay how they get on in creche of pre-school,” she said.
“It will mean they won’t be able to partake in the same kind of schoolwork that other children might be able to. They will struggle and fall behind other children when there really is no need for them to.
“If you get in there early, there is no reason why the child can’t participate the same way any other child can in the school setting.”
Of the children waiting two years or more, 384 are in CHO 7 (Community Health Organisation 7) – which includes Kildare, west Wicklow and parts of Dublin.
Meanwhile, 1,085 children in north Dublin have been waiting at least a year for their first assessment.
Many other regions throughout the country also have long waiting lists.
Yesterday, Newstalk revealed that just under 21,000 children are waiting for their first assessment with an occupational therapist – more than half of them for longer than one year.