Han, Job, Kukin and Fabiana were poorly and hadn't had enough to eat or drink when they were found.
They were rescued by marine biologists and spent two months at a special rehabilitation centre in Peru in South America.
Carlos Yaipen, one of the experts who helped make the the creatures better, says he's found lots of sick sea lions and believes changing sea temperatures are to blame.
He said: "These sea lions are survivors of various illnesses which they contracted off the coast of Peru caused by the phenomenon of El Nino.''
The little creatures were taken by boat to Palomino island, in Callao, Peru for their release, which is home to over three thousand other sea lions.

With just under 600 objects from the 1820s to 2007 on show, the lid will also be lifted on some lesser-known and often gruesome tales.
Evidence from the Metropolitan Police's Crime Museum - also known as the Black Museum - will reveal "London's amazing hidden stories" in an exhibition from October.
A briefcase, syringe and poison belonging to the Kray twins, and secret microdot messages that exposed the Portland Soviet Spy ring, are just some of the objects visitors will be able to see that have previously been behind closed doors.
A published memoir containing handwritten notes in the margin by Donald Swanson, senior investigating officer on the Jack the Ripper investigation, will also feature in the exhibition.
Swanson reveals his personal thoughts, naming Aaron Kosminski as prime suspect for the unsolved murders.
"This is an amazing hidden story for London," Museum of London content director Finbarr Whooley said.
"For 140 years, the Metropolitan Police has amassed a fascinating collection of real objects and evidence from the UK's most notorious criminal investigations that until now have been behind closed doors."
In a case bringing museum visitors up to speed on more modern evidence gathering techniques , a laptop retrieved from the burning car which  crashed into Glasgow Airport in a 2007 terrorist attack will also be on show.
Despite the laptop being badly burnt and damaged, more than 90% of its data was retrieved, which was used to link the case to the attempted car bomb attacks in London the previous day.
Among the more unusual items being revealed are the gallstones of Olive Durand Deacon, a wealthy solicitor's widow who was charmed by entrepreneur John George Haigh while staying at the Onslow Court Hotel in Kensington, west London, in 1949.
Little did she know that her new acquaintance already had the blood of five murder victims on his hands.
Haigh lured Mrs Deacon to his West Sussex workshop before shooting her in the back of the head and dissolving her body in acid in an act closely resembling a modern day scene from gritty US sitcom Breaking Bad.
With no body to be found as evidence, it was down to a shrewd detective who spotted pebbles on the workshop floor - it later transpired these were Mrs Deacon's gallstones.
The gallstones will be on display  alongside the remains of Mrs Deacon's gloves and handbag.
But with all of this intriguing evidence on display, is there a risk of forgetting about the victims and glamorising the crimes?
The Victims' Commissioner for England and Wales, Baroness Newlove, thinks the exhibition carefully avoids this trap.
"I am pleased the exhibition recognises that their voice is central when investigating and prosecuting crimes," she said.
Met Police assistant commissioner Martin Hewitt agreed and said: "I'd be very disappointed if anyone went away thinking we were glamorising these crimes."
A telling example of evidence that puts the tales of the victims who suffered at the centre of these crimes are artefacts from the 1979 Spaghetti House Siege in Knightsbridge, west London.
Hostages were held for five days after gunmen burst in to the restaurant chain as staff were gathering to collect the week's takings.
Alongside a balaclava and hat worn by gunmen involved, notes written on napkins by the hostages will be displayed.
After it emerged one of the hostages had taken ill, a restaurant manager offered to substitute himself for the victim.
"While the cases illustrate the worst in human nature, they also show the humanity," exhibition curator Julia Hoffbrand said.
The Crime Museum Uncovered exhibition opens at Museum of London of 9 October
Four sea lions have returned to the ocean after being nursed back to health.
[NEXT_CONCEPT]
From Jack the Ripper investigation notes to a bottle of Veuve Clicquot champagne belonging to the Great Train Robbery gang, a fascinating collection of evidence amassed from some of the most notorious crimes in the UK is to go on public display for the first time.