The Irish Nurses Organisation has said 3,000 fewer children will be treated at Our Lady's Hospital in Crumlin this year if the Health Service Executive proceeds with planned cutbacks.
Three wards and two operating theatres will be closed in a bid by the HSE to reduce a deficit of €9.6 million.
Up to 200 people held a protest calling for a reversal of the decision.
The protest came two days after a 25 bed ward - St Joseph's - was closed at the hospital.
It is the first of three wards that will close before August as part of cost-cutting proposals at the hospital.
Two operating theatres will also close in July and August.
The INO says the cutbacks will significantly impact on patient services, especially in the busy summer months.
The HSE told RTÉ news it is working with Dublin's three paediatric hospitals to maximise resources.
Organisers of today's march say they will hold another protest in two weeks time.
Separately, the Health Service Executive is urging the Irish Nurses' Organisation to call off a strike at Sligo General Hospital next week.
The HSE said it has been advised nurses will hold a 12 and a half hour strike on Wednesday six days after a ten-hour strike was staged at the hospital.
Nurses are protesting over what they say are low staffing levels.
The HSE said it is satisfied that current nursing staffing levels at Sligo General Hospital are sufficient to meet patients' needs.
