Sisters Avigail and Yael Gross, ages 2 and 4, were killed by the poison. Their brothers, Michael and Yitzchak, ages 5 and 7, are in extremely serious condition, Arutz Sheva reported.
"How could I be on a day like this? Two victims, two innocent little lambs," the children's grandmother, Tzippora Gross, said.
She urged listeners to pray for the boys, and said the parents of the children are also very ill due from the pesticide that was used in their home.
It is unclear if the parents will be able to attend the girls' funeral, set for 1:30 p.m. in a Jerusalem cemetery.
The exterminator who allegedly left pesticide in the home has been arrested for negligence, Arutz Sheva said.
The pesticide has been identified as a type of phosphine, the same material used in Syria's chemical weapons.
There is no antidote for the deadly poison.