A five-year-old boy who was found dead in a river in south Wales has been described as a bright, cheerful child whose smile “lit up the world”.

Police named the boy as Logan Mwangi – also known as Logan Williamson – who lived in a flat close to the river in the village of Sarn, near Bridgend, where his body was discovered.

A 39-year-old man, a 30-year-old woman and a 13-year-old boy have been arrested on suspicion of murder after Logan’s death, South Wales police said. The force’s major crime team is investigating.

The boy was found in the River Ogmore on Saturday. Since then, police have been trying to find out where and how he died and how he ended up in the shallow river. On Monday morning, police forensics officers continued to work at the ground-floor flat where the boy lived, 400 metres from where his body was found.

Neighbours and friends left cuddly toys, messages of condolence and pictures close to the river bank.

One woman, who asked not to be named, said Logan was her daughter’s best friend. She said: “He was smart, intelligent, happy, polite. He had a smile that lit up the world. He didn’t deserve this.” Her daughter left a drawing she had made of the boy, with the message: “Logan, I love you.”

Lois Sheppard, whose daughter, Maisie-Rae, left a tribute to Logan, said: “This is a tight-knit community and we’re all absolutely gobsmacked.”

Some neighbours reported hearing a row at Logan’s home on Saturday.

The boy was taken to the Princess of Wales hospital in Bridgend, where his death was confirmed.

A statement from South Wales police said: “We can confirm that following reports of concerns for a missing five-year-old boy in Sarn, Bridgend, and the subsequent finding of the body in the Ogmore River, three people have been arrested.

“A 39-year-old man, 30-year-old woman and 13-year-old boy, all from the Bridgend area, have been arrested on suspicion of murder. We are not looking for anyone else in relation to this incident.”

Police have called for witnesses who were in the area at 5.45am on Saturday to come forward with information.

Ch Insp Geraint White said: “This is a tragic incident in which a young child has sadly lost their life. We are appealing for anyone who may have witnessed this incident, or who has any information, to get in touch. We would ask the public not to speculate about this incident on social media as this is an active investigation.

“If you have any information that can help, please report this to us. Our thoughts are with the family and we are supporting them in every way we can.”