Almost 350 children were treated for obesity in HSE hospitals in 2017 and 2018.
The new figures have been released under the Freedom of Information Act.
The HSE's statistics show the number of children who had a principal or additional diagnosis of obesity when they were discharged from statutory hospitals.
199 children fell into this category in 2017, and 145 the following year.
Professor Niall Moyna from DCU's School of Health and Human Performance said: "It is alarming, but I think there certainly is a lot more public health initiatives and that's really what's going to work at a public health level.
"We're talking about 350 kids but we have to educate the general population and I think parents are a lot more aware.
"There is a big socio-economic influence on the risk of developing obesity in childhood and we see it much more in lower socio-economic groups."
The stats include inpatient and day-case stays only, not emergency department or outpatient cases.
Safefood, the food-safety promotion board, said that in the short term, childhood obesity can cause problems with bone health, breathing difficulties, and psychological and social issues.
In the long term, it can cause cancer, heart disease and diabetes.