A Michigan family has been left heartbroken after two of their children were struck by an SUV and died.

Karalee, 13, and Calvin Shepard, 12, were riding their bikes in their Williamston neighborhood, near Lansing, when the vehicle plowed into them at around 11.30am on September 5. 

A 64-year-old woman driving a Ford Explorer hit the children, killing Calvin at the scene and leaving Karalee with life-threatening injuries.

On Thursday their mother, Raquel Roark Shepard, announced her daughter had also died from 'complications resulting from the accident that took her brother Calvin just five days ago.' 

'She was surrounded by her family and deeply loved until her final breath,' the mourning mother wrote on Facebook.  

'Our hearts are broken beyond what we can put into words. We find comfort in knowing that Karalee and Calvin are together again and in the loving arms of our Savior.'  

Both children were wearing helmets at the time of the crash and were riding along the shoulder of the road.

The driver was unharmed and stayed on the scene until police arrived. Police do not believe drugs and alcohol were involved in the crash.

No one has been arrested as of Friday morning. 

The children's joint funeral will be held on Tuesday, Raquel said. 

'We simply cannot bear the thought of saying goodbye to our children twice,' Raquel said when she announced Calvin's funeral would be moved to the same day as Karalee's.  

The mother-of-six remembers her young son for his approach of taking life 'head-on.'

'He had just started middle school and was so excited to share that experience with Karalee and have her show him the ropes,' she wrote on Facebook. 

A family friend started a GoFundMe to help support the Shepard family. 

It has raised more than $137,000 as of Friday morning. 

The Daily Mail has reached out to the family and the Michigan State Police for comment.