Police in Midlothian are appealing for witnesses following a three-vehicle collision in Dalkeith.
The incident happened around 4.50pm on Thursday 15th August on Easthouses Road.
A Ford Transit van travelling south was involved in a collision with a Mitsubishi Outlander, which was in front, before then colliding with a Vauxhall Vivaro van travelling North.
The 34-year-old male driver of the Transit was taken to the Royal Infirmary of Edinburgh for treatment to an arm injury before being arrested in connection with the collision.
Three girls aged 13, 9 and 5 were also within the Transit, along with a 7-year-old boy.
The 9-year-old sustained significant injuries to her head and leg and was taken to the Sick Kids Hospital where she remains in a serious condition.
The other children sustained only minor injuries, as did the male driver of the Vauxhall Vivaro.
Occupants of the Mitsubishi were uninjured.
Inspector Andy Gibb from the Road Policing Unit in Dalkeith said: "While we have one man in custody following this collision, we are still conducting our inquiries to establish the full circumstances and would ask other motorists who were on the road at the time, and witnessed what happened, to contact police immediately.
"Likewise, if you believe you have any relevant dash-cam footage capturing the incident, then please also come forward."
Those with information can contact the Road Policing Unit in Dalkeith via 101 and quote incident number 2867 of the 15th August.