Lindsay Reed, 35, of Kings Barn End, Steyning, was visiting Shoreham Beach with her three children, Jamie, five, Samantha, nine, Megan, 14, and Megan’s friend Jade, 14, at around 5.45pm on Sunday evening when the incident happened.
Megan and Jamie were headed in the direction of the sea, close to some rocks when Jamie fell.
What happened next has left Lindsay having flashbacks ever since.
Megan said: “The sand just looked flat. It didn’t look watery or anything. He walked across it and tripped and his foot got stuck.
“At first I thought he was okay, but then he started drowning. He kept getting lots of sand in his mouth and ears.
“I tried to pull him out and grab his arms,” said Megan.
She added that one of her legs got trapped during the rescue attempt and sank down to her knee, before she managed to free Jamie.
Lindsay said: “It happened within a split second. I glanced over at my other daughter, glanced back and he had gone.
“I have had a lot of flashbacks over the last couple of days. He was terrified. I’m so glad she managed to get him out. I just wish I had been the one to pull him out because he’s my little boy.
“I’m very proud of my daughter for getting him out. If she hadn’t have been there I dread to think what would have happened. We have all told her how proud we are.
“I have never witnessed that and we go down to the beach quite a bit.”
Following the incident, Lindsay is keen for signs to be erected warning of possible dangers.
“I think with summer and the amount of kids that are going to go down there it needs to be addressed,” she said. “There could be more of them.
“If I had lost him I would have been devastated to be honest. I want to make sure people know it’s there.”
Jade also tripped and fell into the same patch of sand and sank down to her waist, according to Megan.
Lindsay added: “My daughter’s friend fell in the same hole. Her being taller she managed to pull herself out. It came up to her waist. “
Recalling the moment Jamie fell, Lindsay said: “He sort of tripped and fell in face first. He went over on his belly. He was struggling to get out and flailing his arms around to get out. My daughter said all you could see was his face above the sand. She was trying to pull his arms and it went up to her about her knee.”