Four boys, between nine and 10 years old, were arrested in Punggol on Tuesday afternoon for suspected vandalism.
The boys - three in Primary Four and one in Primary Five, are understood to be from a primary school in the vicinity.
They are said to have spray-painted objects with profanities as well as "O$P$" - short for "owe money, pay money", typically used by loan sharks and runners.
Police said in a statement on Thursday that investigations are ongoing.
Preliminary checks have shown that a total of four vehicles, a bicycle at at a multi-storey car park at Block 169 Punggol Field, as well as walls and letter-boxes at the neighbouring block of Housing Board flats, Block 168C, were spray-painted in various colours.
Police responded to a call at 2.15pm from Mr Benjamin Lei, 33, who was visiting his in-laws who live in the neighbourhood. The regional sales executive had said that he had detained four boys, who he believed had vandalised a car.
He told The Straits Times: "I didn't witness what they did, but something told me they were up to no good. When I was approaching them, they said 'quick, quick quick'. I saw them trying to hide some cans."
Then he turned around and saw a car parked metres away had been spray-painted. He stopped the boys and called the police. "They were compliant when I told them to stop. I think they might have been too scared to run away."
The offence of vandalism carries a maximum punishment of three years in jail or a fine of up to $2,000, and caning. But courts typically seek to rehabilitate juvenile offenders, either via probation or detention in a home.