He is currently receiving intensive care at Tan Tock Seng Hospital.
The devices carried by passengers, crew or via mail for non-commercial purposes are allowed.
The victim's father and five-year-old brother were also struck by the slab of cement.
A consumer who purchased the product "experienced immediate and effective results".
One of the pilots who operated the drone did not possess an unmanned aircraft pilot licence.
He spent about 5 minutes outside the door and tried to unlock the gate three times.
Mr Lee Hsien Yang is "trying to create a false urgency" by pushing for immediate demolition, the Government said.
A white Hyundai had stopped in the middle of the road.
There were no casualties as a result of the collision.
Investigations are currently ongoing.