The 13-year-old was found slumped in the street with serious injuries and was later said to be in a critical condition in hospital.
A 16-year-old has been arrested and will appear at Kilmarnock Sheriff Court today in connection with the incident in the town.
Police said earlier they were treating the incident as attempted murder.
The boy was found at the side of the town's Odeon cinema at 2.40am yesterday.
Police sealed off the area around the cinema while forensics experts carried out a detailed search.
Restrictions were placed around a section of road between the Odeon and Lawson Street.
Residents said they heard footsteps and shouting around the time of the incident.
One woman, who did not want to be named, said: "This is a pretty busy area in the early hours with people returning from nights out. I could hear a commotion outside when I was watching television.
"There was footsteps and raised voices, but I couldn't see anyone."
The youngster was taken to Crosshouse Hospital in the early hours.
Meanwhile, police in Glasgow are probing an incident after a taxi driver was threatened and robbed.
The 43-year-old picked up three men in Dennistoun around 1.25am on Saturday, who snatched the cash when the vehicle stopped outside a BP filling station.
The man was unhurt but was left extremely shaken.