North West Ambulance Service (NWAS) said they were called at 3.50pm on June 24, and sent a rapid response vehicle and an ambulance to the scene.
A spokesman for Lancashire Fire and Rescue Service said: "Swift water rescue technicians entered the water and rescued the two people using a rescue sled and a first aid kit.
"Crews were in attendance approximately one hour."
NWAS said both children were okay and neither needed hospital treatment.
Paul Simpson, Water Lead at Bowland Pennine Mountain Rescue Team has previously issued advice on water safety.
He said: "Reservoirs, rivers, disused quarries and other water bodies can be perfect places to visit, but they can be dangerous.
"Water may look safe, but it can be hazardous, which is why it's important to spot and keep away from dangers.
"It's important to continue to follow the latest health advice, including about social distancing, even when outdoors."
RISKS AROUND WATER
Unattended waters like rivers, lakes, and reservoirs and out-of-bound areas such as quarries, can seem like exciting places to explore. But they can be full of dangers.
The dangers of water include:
Wery cold temperatures - the water can be colder than expected, even in warm weather
Hidden currents - there can be strong underwater currents, which can trouble even the most confident of swimmers
Reservoirs are often very deep - it is difficult to estimate depth and they can be deeper than people expect
There may be hidden debris or underwater hazards which can cause injury, including weeds and plants which can entangle people under the water
It can be very treacherous underfoot especially around the water margins and difficult to get out of the water ie-steep slimy banks
Water quality can also be poor with stagnant water and the proliferation of algae and this can sometimes be hazardous to health.