US-made bomb used to killed civilians in Saudi-led airstrike on Yemeni residential building, says Amnesty
It's findings come following an analysis by arms experts.
Her parents and five siblings were among those killed by the bomb.
Amnesty urged the US and other Western states to implement a "comprehensive embargo" on the sales of weapons to member of the Saudi-led coalition in the war-torn country.
"It has time and time again committed serious violations of international law, including war crimes, over the past 30 months, with devastating consequences for the civilian population."
In December 2016, the US administration under then president Barack Obama blocked the transfer of precision-guided bomb kits to Riyadh.
A senior administration official said the move reflected "strong concerns with the flaws in the coalition's targeting practices" and its overall conduct of the Yemen air war.
US President Donald Trump has stepped up military support to Riyadh since taking over from Obama.
The US and Saudi Arabia in May announced an arms deal worth almost $110 billion, described as the largest in US history.
The Saudi-led coalition, which waged a war against Yemeni Houthi rebels in March 2015, has been repeatedly criticised for attacks on civilians.
It admitted to carrying out the deadly attack in August but claims civilian casualties were a result of a "technical error".
Buthania, who is now in the care of her aunt and uncle, made headlines after a photograph captured her trying to open her swollen eyes while lying on a hospital bed went viral.
The five-year-old girl became a symbol of the plight of Yemenni children, sparking a social media campaign under the hashtag #BouthainaTheEyeOfHumanity.
Hundreds of social media users share pictures of themselves mimicking her gesture closing one eye and trying to open the other.
The conflict in Yemen has killed more than 8,000 people, including at least 1,500 children. It has also displaced millions, pushing the impoverished country to the brink of famine.
The UN warned in July that 80 percent of Yemen's children desperately needed aid in what the organisation has called the "largest humanitarian crisis in the world".
Agencies contributed to this report.