The two children killed in a Desert Rd crash on Friday were boys, one aged 2 months, and one 4 years.
They were 4-year-old Arteen Mosaferi, and Radeen Mosaferi, who was 2 months old.
The boys were from Hamilton.
Arteen died at the scene and Radeen died at Starship Hospital yesterday from his injuries.
Another person involved in the crash remains in a critical condition in Waikato Hospital.
The Serious Crash Unit and the Commercial Vehicle Safety Team are investigating the crash, which involved two cars and two truck and trailer units.
Police were called to the crash, between Waipakihi Rd and Rangipo Intake Rd, about 3.30pm on Friday.
The boys were correctly restrained in car seats.
The Easter weekend road toll is four, which is twice as many than the total number of road deaths for the holiday last year.
Another crash on Friday in Tirohanga, between Pokuru and Tirohanga Rds, north of Taupo, killed Taupo woman Denise Tito.
Tito was grieving the loss of her mother and will share a double funeral with her.
On Saturday morning, a person died after a motorbike and truck collided in Rotorua.
Horrified crash witnesses said the motorbike lost control and went under the truck's wheels.
The motorcyclist died at the scene despite frantic efforts from members of the public to resuscitate him.
The official Easter holiday period began at 4pm Thursday, March 29 and will end at 6am tomorrow.
Traffic is expected to be heavy in places around the country today as people return from holiday and authorities are pleading motorists remain patient and alert.
NZTA has created maps to show the expected peak holiday traffic to help motorists decide the best time to travel to avoid queues.
The busiest areas and times are based on previous years' travel patterns.
Returning traffic will be heavy in those areas from this morning to Tuesday evening.
Other North Island hotspots include Bay of Plenty, Coromandel and Waikato.
NZ Transport Agency safety and environment director Harry Wilson said with more people on the roads it was important to plan ahead.
"We don't want to see people getting impatient and taking unnecessary risks such as dangerous overtaking manoeuvres or following too closely."
Police said yesterday that drivers should consider leaving early in the morning or later in the evening to avoid peak travel times.
"Police want everyone to get home tomorrow safely after their Easter break, and ask that motorists take a moment to think carefully about their journey.
"Exercise patience in periods of heavy traffic. When you are on the roads, avoid distractions which can have dangerous consequences for yourself, your passengers and other road users," police said.
Police also recommend drivers are well rested to avoid fatigue.
"Each and every driver has a responsibility to themselves and everyone else on the road to ensure they make it to their destination safely."