When Cooper gets into trouble, Noah or Xavier will cry on his behalf.
And when the three of them are separated they seem to panic, and plead to be reunited.
It is the kind of solidarity borne of nine months together in the same womb.
The boys - identical triplets from Albion Park - will celebrate their third birthday tomorrow with a visit to the Illawarra Light Railway.
They share a love of trains, but it is their differences that parents Lisa and Keiran Billing are eager to see recognised as they grow.
Xavier is the responsible one; intelligent and fond of technology.
Clever Noah is the most inquisitive and seems to absorb everything he sees, while Cooper is the charmer, and the most likely to start trouble.
In the lead-up to Multiple Birth Awareness Week, March 10-17, Mrs Billing told the Mercury she never dressed the boys identically and planned to enrol them in separate kindergarten classes to give them the best chance of "forming their own personalities".
"They know they're different," she said.
"I don't want them to grow up feeling self-conscious over being triplets."
The triplets are identical and naturally conceived, a combination of rarities thought to occur once in every 160,000 births.
None has unique birthmarks or distinguishing features but Mrs Billing can instantly tell apart the boys' faces and their cries.
She cried herself after learning she was carrying three babies and, with Mr Billing, was repeatedly warned of the likelihood of complications, including the possibility of losing one of the babies.
But the delivery was smoother than expected and so too was life with three babies, all good sleepers and non-fussy eaters.
The Billings renovated their garage into a new bedroom big enough for the three boys.
In July, they started attending preschool two days a week, to give Mrs Billing some time off.
But she countered the view - offered freely by strangers at the shops - that "you must be ready to be put into a mental institution if you have triplets".
"People just assume the worst when they see multiples, but it's one of the most beautiful things," said Mrs Billing, who is also a mum to Lily, 8, and Aidan, 11, from a previous relationship.
"I always say 'if you don't have triplets you're missing out'."