The two-alarm blaze was reported at 10:53 a.m. at the LeMar Trailer Park at 1933 E. Bayshore Road.
Redwood City spokesman Malcolm Smith said firefighters controlled the fire in less than an hour. The blaze destroyed one trailer and a car, and damaged two other trailers, he said.
The 12-year-old girl was taken to the hospital as a precaution, Smith said.
He said seven people were displaced from one trailer, and four people were displaced from each of the other two trailers that burned.
The American Red Cross is assisting the displaced residents.
Damage was estimated at $135,000 and the cause remains under investigation, although Smith said the fire appears to have been accidental.
He said about 40 firefighters responded to the blaze.