The regulation will be particularly in force in districts 1, 9, 12, Binh Thanh and Binh Tan.
The move is part of activities by the city's Traffic Safety Committee on the implementation of a three-year national programme.
While helmets reduce injuries by two thirds and cut fatalities by nearly half, most parents ignore buying them for their children.
About 10,000 leaflets are issued today along with 500 posters and 120 panels.
The programme aims to boost the ratio of children wearing helmets to at least 60 percent by the end of this year.
Latest WHO statistics show that 77 percent of adults wear helmets but only 32 percent of children.
Each year, about 1,000 children die and 2,000 others are injured in traffic accidents.
By law, children aged six and over must wear a helmet when travelling on a motorbike.