A 10-year-old girl and her grandparents were thrown into the sea when their boat capsized near Hardway, Gosport, on Saturday. The girl was taken to hospital as she swallowed seawater.
The grandmother and the girl were pulled out of the water by a yacht passing by, and the grandfather picked up a smaller ship that helped catch their things from the sea.
However, one bag, containing two plush ones, disappeared during the rescue, and now the family is desperately searching.
A lifeboat of the coastal rescue service Gosport and Fareh and two police boats were called to help.
The lifeboat was launched by HM Coast Guard about 16 hours after an incident near HMS Monmouth, which is moored at Lake Farham, Gosport.
Arriving at the scene, lifeboat paramedic Richard Brady was transferred to the rescue vessel and assessed the victims.
He said: “All three were in the water and the young girl swallowed a significant amount of seawater.
“It can be very dangerous because there is a risk of secondary drowning, so she was transferred to an ambulance crew that took her to the hospital.”
Both grandparents were warmed and treated for shock.
Ruble lifeboat Gafirs James Begott said: “All three were very lucky that a yacht passing by saw what was happening and helped.
“We should thank the crew of this ship for their help, because they undoubtedly saved the situation from escalation.
“After we helped the family, it turned out that the bag with two plushes, which the child loved very much, was lost.
“If anyone notices this, they can contact the Gafirs team through our website and we will help reunite him with his family.”
A statement about the missing bag and plush plush was also posted on Facebook, and sailors are being asked to follow it on the shoreline.
The incident was one of five gaffes attended during the platinum anniversary weekend.
So far this year, an independent lifeboat service – not part of RNLI – has been launched 47 times in Solent.