Police are warning trick or treaters that throwing eggs and flour could be considered criminal damage or assault.
Croydon police and Croydon Council launched a new initiative to deal with antisocial behaviour during Halloween and Bonfire Night on Friday.
The initiative will see an increase in police patrols throughout the borough.
Safer Neighbourhood Teams will visiting shops to ask them to be wary of selling eggs and flour to teens in the weeks before Halloween.
Officers are also advising trick or treaters to only go out with an adult, stay in well lit areas and only visit the homes of people they know.
Police are also warning acts of vandalism such as throwing eggs could lead to stiff penalties.
Inspector Peter Salter, of Croydon police, said: "Halloween and Bonfire Night should be a time for celebration and fun but unfortunately for a small minority this time of year is often used as an excuse for intimidating behaviour and striking fear into the elderly community."
Police and trading standards officers will be visiting shops selling fireworks to check their licenses, and making checks to ensure stores are not selling alcohol to under-18s.
Councillor Steve O'Connell, deputy leader of Croydon Council, said: "A well organised public firework display or small private party can be enjoyable for all the family but in the wrong hand fireworks can be a danger and a nuisance."
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