Firework attacks on three homes in the last week have prompted calls for parents to make sure their children know how dangerous they can be.
Police and fire officers issued the warning after lit fireworks were shoved through the letter box at a Hounslow property last Friday evening, one in Chiswick, at around 6.30pm, on Monday, and another at a Feltham home at 7pm, on Tuesday.
They believe unsupervised children were probably to blame for the pranks, which could have caused fires at the properties.
Insp Manpreet Bains, of Hounslow Police, said: "Hounslow Police would like to appeal to parents to advise their children about the extreme dangers of pushing fireworks through letter boxes.
"Some children might see it as a bit of fun, however, this is an extremely dangerous practice and can easily lead to serious injury and damage and even fatality. We've been very lucky so far."
No one was injured in the three incidents but police and firemen are concerned that the problem may escalate in the run-up to Bonfire night, next Wednesday.
Chiswick Fire Station Manager Rhodri Horton advised people to go to an organised display rather than buy their own fireworks.
He added: "This is a busy time of year for London Fire Brigade, with crews seeing an increase in fires caused by out of control bonfires, or fireworks. If you do buy them yourself, then follow the firework code. Fireworks burn at thousands of degrees and can easily cause damage to property, or worse serious injury, if thrown or used incorrectly."