The three victims were rushed to Mayo General Hospital in Castlebar. The girl was transferred to Dublin for emergency treatment.
It followed a single car crash yesterday shortly before 4pm in which a 42-year-man was killed on the Tullow to Castledermot Road in Co Carlow.
The man was pronounced dead at the scene.
Meanwhile, a 29-year-old man was killed on Saturday in a single vehicle crash in Granagh, Co Limerick.
The collision occurred at 3.55am on the Croom to Granagh road at Kilmore.
Gardai have appealed for witnesses.