The search for the two adult boaters was suspended late Saturday night, but resumed Sunday morning, The St. Louis Post-Dispatch said.
The missing adults were not wearing life jackets when the boat overturned Saturday, officials said.
The boat carrying the boy and the two adults capsized at 1:45 p.m. near Hartford, Ill.
Occupants of a nearby towboat pulled the unidentified boy from the water, the Dispatch said.
The boy was taken to a hospital and he is expected to survive.