Charity The Voice of Martyrs has heard from witnesses about the 'well-planned' assault on Attagara at the start of June.
More than 100 militants entered the village just as Sunday church services started, opened fire and started attacking people with machetes.
The organisation spoke to 55-year-old Sawaltha Wandala who witnessed Boko Haram killing children inside a church.
He claims to have seen one militant throw a child into a ditch after having been severely slashed.
When he tried to help the boy the terrorists grabbed him and beheaded him.
The Islamists then returned to the village two days later to continue the attacks.
It's thought an estimated 200 people, including young children, were killed.
Boko Haram has been leading a campaign of terror against Christians across Nigeria in recent months.
The group's name means Western education is forbidden and it's leader Abubakar Shekau, pictured, says its aim is to introduce Sharia law.
It's thought Boko Haram has killed more than 5,000 civilians between July 2009 and June 2014, including at least 2,000 in the first half of 2014.
In April the group abducted more than 200 school girls from classes in Chibok and many of them are still missing.
A video has appeared online claiming to show the girls being forced to convert to Islam.
In it, the militants threatened to sell the girls into slavery or as child brides.