The sheriff's office stressed that boaters and swimmers should wear a properly fitted life jacket whenever they are on the water.
They are two of the six people who lost their lives during Tropical Storm Chantal.
The two people entered the water around 5 p.m. on Sunday, and their unoccupied canoe was recovered later that evening.
The child's identity is not being released at this time, the sheriff's office says.
A bystander jumped in and tried to help, but the woman and her daughter were unresponsive, officials said.
A Princeton University undergraduate student who had been missing since last weekend has been found dead, the school said in a statement Friday.