A baby boy with a "joyful smile" was killed when a van mounted a pavement and struck his pram.
Five-month-old Louis Thorold died following the collision on the A10 in Waterbeach on Friday, Cambridgeshire Police said.
His 36-year-old mother Rachael Thorold, who was pushing the pram, is in hospital in a critical but stable condition, the force said.
Police have released a photo of Ms Thorold holding her smiling son, with the picture taken just hours before the collision.
A grey Mazda 2 was in collision with a white Renault Master van, and the van hit Ms Thorold and her son's pram.
Police are investigating what happened.
Ms Thorold, of Gibson Close, Waterbeach, is currently on maternity leave from her role as a planning policy manager for Elmbridge Borough Council, which has its main offices in Esher, Surrey.
She was taken to Addenbrooke's Hospital in Cambridge following the collision, which happened at around 3.50pm.
The driver of the van and the driver of the Mazda suffered slight injuries and remained at the scene.
Louis's father Chris Thorold, who is the finance director of Marshall Aerospace, said in a statement released through police: "We will love you always our little Louis.
"You were only with us for a short time, but you made us the happiest people in the world.
"I cannot describe how heartbroken we are that you are gone.
"You are such a happy little boy and your joyful smile and laughter will never leave us.
"Your ma-ma is fighting to stay with us and we are praying that she will make it through.
"You will always be in our hearts and do not worry, I am taking care of all your animals.
"We love you so much and we know you will now be safe with granny, grandad and great grandpa in heaven.
"Take care my little Lou, sweet dreams."
Police are appealing for witnesses or anyone who may have dashcam footage of the collision or moments leading up to it.
Detective Sergeant Mark Dollard, from the road policing unit, said: "This is an extremely tragic and sad incident and our deepest condolences go out to the family of Louis, who are being supported by a specially-trained officer.
"A thorough investigation will now be conducted by my team and I am seeking help from the public.
"While it is too early to say how the collision happened, I want to remind all road users of their responsibilities to drive with care."
Anyone with information should call 101 or visit www.cambs.police.uk/report quoting incident 278 of January 22.