Snug locals Jobie (10) and Lily (14) were swimming at Snug Beach when they saw some tiny blue plastic pellets washing up on the beach.
When they looked properly, they said they could see that it was all over the sand.
"After dinner, my brother and I went back down to the beach, and it took us a few hours to collect it all in some buckets," Lily said.
"Then we took it home, put it in a bag so all the pieces wouldn't spread out again and put it in the bin."
Greg, another local who was walking his dog along the beach, said that the children had cleaned 150 metres of beach all by themselves.
The family usually tries to pick up rubbish when they're out walking or having a swim.
They say they love the beach and being in nature and having rubbish around really spoils it.
The children have learned about the way plastic gets into the food chain and all the suffering this causes for animals.
The family has joined the Snug Landcare group's regular working bees on occasion but the parents said their general philosophy is to leave places better than they found them.
"We love and enjoy the natural beauty surrounding us in Snug (and the rest of Tassie), and if there are even just little things we can easily do to keep it pristine, then why wouldn't we?" they said.
"We're really glad to see the kids just naturally wanting to look after the world around them, and we hope they'll take that optimism and passion with them into the future."