Harrison Keeley attends Park Avenue Nursery in Deal, and as part of one of their activities, eight children wrote letters and drawings and put them inside a bottle to send off Deal beach on Friday 19th June.
Harrison drew a picture of an octopus and the nursery put the address and date and asked whoever found it to let them know how far it had gone.
On Tuesday 23rd June, it was found by the Recreational Diving Society in De Haan, a seaside resort between Ostend and Zeebrugge.
The group were taking part in their annual rescue training.
Member Rik Demeyer said: “The sea was very rough and one of our members lost a fin. While looking for it, she found a sealed little plastic bottle with a message.
“As scuba divers, we always recover plastic objects from the sea. This message said it came from the Park Avenue Nursery and After School Club in Deal.
“It was a letter from Harrison, aged four, and contained a drawing of an octopus. It had travelled 70 miles across the sea.”
Evelyne Becu, who found the bottle, sent a letter back to the nursery to let them know it had been discovered.
In her letter, Mrs Becu said: “We were all so very charmed by your beautiful drawing of an octopus.
“We were surprised to discover that you send us a drawing of an octopus as we often encounter them on our scuba diving trips. They are really very beautiful and amazing animals.
“So, dear Harrison, I would like to thank you for your beautiful letter.
And in return I send you a copy of the local paper and a drawing of an octopus made by my daughter Jeanne (aged 7).”
Stephanie McGahan, proprietor at Park Avenue Nursery said she hadn’t expected a response.
She said: “They’d been learning about pirates all week. On a Friday afternoon the children go out and do something and they thought they would write a letter and put it in a bottle. They all did one.
“We didn’t actually think they would be found.”