New figures show that 247 children have been waiting at least two years for an initial speech and language assesment.
A further 438 children have been on the list for more than 12 months.
Cork, Kerry, Dublin, Kildare and Wicklow are among the worst affected areas in the country.
The Irish Medical Oranisation has said children's development is being badly affected by the waiting lists for speech and language therapy.
The HSE has said its service plan for this year provided for 100 new therapy posts, including speech and language therapy, but IMO's GP committee Dr Martin Daly has said it is not having an impact on waiting lists:
"This is a major problem," he said. "These waiting lists mean that children do not get early intervention in time and it does affect their education development."
Suzanne Connolly from children's charity Barnados is calling for urgent recruitment of more speech and language therapists to address long waiting lists.
"I also think we need to look at potentially the management of the speech and language therapy service. We need to understand what are the differences in different areas: is it to do with demand or is that to do with actual services being managed?"
Parents are being forced to pay for private speech and language therapy because of huge waiting lists for public treatment, according to the Children's Rights Alliance.
According to details released under the Freedom of Information Act, 417 children have been waiting more than 18 months for an initial assessment with the HSE.
The HSE says it aims to see all patients within a year and so far in 2019, this target has been met in 92 per cent of cases.
But Saoirse Brady, from the Children's Rights Alliance, says many people opt for care elsewhere because of the long waiting times.
"Parents are actually paying privately to get their child assessed and get treatment quickly.
"We've heard from parents where a child has been told that they have to wait a year to be assessed and then another year for treatment, whereas if they got that treatment in the interim, then actually they mightn't need anything after the year that has already passed.
"It's vital that we actually support the staff, the service and that we reduce these waiting lists."