"If you promise me you will do something for the children of Syria, I am already your new friend," Bana wrote.
U.K. Labour leadership contender made comments at a campaign hustings.
A London woman delivered hundreds of public messages to the U.N.'s Syria envoy in Geneva.
A human-rights monitor says Russian warplanes carried out the bombardment.
Kerry calls for Putin to examine Assad's actions.
The cessation of hostilities was "a glimmer of hope", Syrian President Bashar al-Assad said.
Syrian President Bashar al-Assad has meanwhile told refugees to come home.
Peace process runs into trouble after Islamic State bombers killed more than 60 people.
A prerequisite for peace is an end to barrel bombs, starvation sieges, mass terror and ubiquitous torture.
An opposition representative said the delegation might turn up if their demands were swiftly met, but the chances appeared slim.
The Syrian conflict has killed more than 200,000 people and will enter its sixth year in March.
The military situation on the ground does not indicate that the Assad regime needs to compromise.
It will be the first time that Tehran attends an international summit on the four-year-long war.