The bodies of the children – aged 1, 2, 3, 6 and 8 – were later found in a run-down flat by shocked cops in Solingen, western Germany.
The children’s older brother, 11, watched the mother, 27, allegedly carry out the horrific killings.
The mum – named as Christiane K in German media – then took the boy on a train journey before she got off at Dusseldorf and threw herself on the tracks.
The 11-year-old was left on the train and continued to Mönchengladbach where his grandmother lived.
He was not harmed and is currently in the care of relatives, police said.
His mother survived the apparent suicide attempt after being rescued by firefighters from between two train track beds at Dusseldorf Central Station – 20 miles from her home.
The deaths of the five children – three girls and two boys – has stunned the local community in Solingen.
The dead children have been named as Luca, 8, and Timo, 6, Sophie, 3, Leonie 2, and Melina who was just one.
A police source told RTL they were poisoned with tablets.
“I really don’t know how desperate you have to be or what must have happened to be able to do that to your children,” said one neighbour.
Another told Bild: “I can’t believe that a mother killed her own children.”
Pictures show several police vehicles and ambulances parked outside the block where cops said they found the five “lifeless” bodies.
Officers frantically tried to resuscitate the children when they discovered the horrific scene, reports RTL.
Those that entered the flat were reportedly left traumatised by what they came across.
Cops last night refused to comment on reports the kids were given tablets by the mother.
However it is reported the child victims had no “physical injuries” and the result of the toxicological investigation is pending.
The mother remains in a serious condition and is thought to be under police protection.
Cops say she is not yet in fit state to be questioned about what happened.
The children’s grandma, who lives 30 miles away in Monchengladbach, is reported to have alerted authorities who later discovered the shocking scene.
Bild reports that the gran claimed her daughter had admitted she killed the five children.
She claimed the mum was travelling with another child, aged 11, with the intention to take her own life.
Police are in contact with the children’s father but provided no other details.
Solingen’s chief of police, Markus Röhrl, told news agency DPA that the incident was “shocking” and that “nothing like this has ever happened to us in the Bergisch region.”
Police spokesman Stefan Weiand called the case “very tragic” adding that he could not confirm how the kids died yet.
He said: “We assume a crime and will have to question the mother about it, but at the moment she is not yet able to be questioned.
“We don’t yet know what exactly happened when and why, only that it is a very tragic situation.
“We can’t say anything about the motive yet. The mother must be interviewed.
“Nothing can be said about the cause of death, it is still being investigated.”
Photos show police officers in white forensics suits going in and out of the horror scene at the apartment block.
One detective was seen with a camera taking pictures on the property’s balcony.
Several green flowerpots filled with plants – some brown and dying – and a small red watering can are littered about the terrace.
Two bikes can been locked up outside the entrance to the apartments.
And chilling pictures also show police tape crisscrossing inside one of the flat’s windows.
Several officers with batons were standing guard as investigators desperately try to piece together what happened.
Local Mayor Tim Kurzbach also arrived to light a candle at the home where the children lost their lives before posting on Facebook.
He wrote: “I am shocked and deeply affected by the news that five dead children have been found in our city.
“I mourn these five lives. And my sympathy goes to all people who are close to the children and the family.
“Today is a day on which we in Solingen are very sad because an act took place that struck us deeply.”
Sources also confirmed the mum is suspected to have killed the children to German news agency DPA.