"It's still too much for him to live anything close to a normal life."
Caleb was suffering up to 60 seizures a day before undergoing brain surgery for a condition that causes epilepsy.
The seizures initially reduced to about every 10 days after the operation in the US in January 2022.
But they have since risen to about eight to 10 a night.
Parents Stewart McCarthy and Kirsty Rosser, from Cardiff, say their surgeon has told them a second brain operation could help Caleb further.
"Directly after the surgery in the US he improved so much," Kirsty told BBC Radio Wales Breakfast.
"We felt like we had a bit of normality back.
"Since then things have started to go back in the opposite direction."
Caleb was diagnosed with epilepsy from the age of three, under-going "months and months" of scans and monitoring by the NHS.
"He was on lots of medication that wasn't really helping," said his mother.
"We were back and forth to the hospital, spending more time there than outside."
Stewart said specialists here were unable to help further, so they looked to the US for help.
"They came to the conclusion that Caleb's seizures were arising from the left frontal lobe of his brain. This enabled them to remove most of the bad area," he said.
Post surgery, Caleb was "doing well for around six months, only having seizures every 10 days in comparisons to multiple nightly previously".
But since then, they have risen to up to 10 a night.
"Although this is still less than when he was first diagnosed, it’s still too much for him to live anything close to a normal life," said his father.
His parents and supporters have, so far, raised more than £14,000 towards the £120,000 costs for a second operation in the US.
"We are really overwhelmed with the support we've had," said Stewart.