The suspects, who hurled a tomato and a marble at the officer from the presidential palace last Thursday, were narrowed down to 15-year-old Louis Sarkozy and a friend he was with at the time, the official told Reuters.
"She said she saw a child's face at the window, without being able to say for sure whether it was Louis," the official said, speaking on condition of anonymity.
Sarkozy is seeking to recover from the worst poll scores of any modern-day French President seeking re-election and the incident marks another potentially embarrassing hiccup in his flagging campaign.
Last week, Sarkozy's entourage was pummeled with eggs and scrunched-up political tracts on a campaign stop in the southern town of Bayonne.
A spokeswoman for the Elysee Palace declined to comment.
The young Louis is not the only Sarkozy offspring to have made headlines in France. Pierre Sarkozy, the president's 26-year-old, rap-loving DJ son, caused a stir in January when he had to be flown home in a government plane from Ukraine where he was due to play a concert, after an apparent bout of food poisoning.