Police are investigating how the toddler came to be left unattended on the bus on February 20.

Officers confirmed they and paramedics were called to 116 Rossi Street, the Yass Little Learners (YLL) child care centre, just after 3pm that day.

Officers said the toddler had been left in the vehicle unattended for about six hours. The temperature in Yass had reached 28 degrees Celsius, outside the bus.

The two-year-old boy was removed from a child restraint seat inside the bus and treated at the scene for dehydration before he was taken to Yass Hospital, where he was kept for observation until 5pm.

On Thursday morning, the boy's mother, Cassandra Brown-Crane, told the Yass Tribune her son, Alijah, was "doing okay".

"I love the centre, it’s a family here," she said. 

"Accidents do happen. Sadly, this could have been tragic, but thankfully he’s healthy and happy.

"I’m very relieved it didn’t end up fatal.

"I’ll remember this day forever and I’m so thankful he is healthy and alive. He bounced back very fast."

In a statement to parents via Facebook, Yass Little Learners confirmed the incident took place on its bus.

The driver was "suspended pending a full investigation by YLL centre management," the statement read.

The statement, released about 9pm Wednesday, went on to assure parents that "every effort is being taken to ensure that a full inquiry is conducted … We will provide a further report of the results of this matter."

But a local parent who asked for anonymity told the Yass Tribune their son had also been neglected in the summer heat on a Yass Little Learners bus two years ago, during his kindergarten year.

The YLL bus driver from two years ago is not believed to be the same bus driver that was recently suspended.

A young child who had alighted from a public school bus had alerted staff to the preschooler's distress; and a complaint was later lodged with ACECQA (the Australian Children's Education and Care Quality Authority), the parent said.

Yass Little Learners director Steve Grundy said the child care centre was "very pleased [Alijah] is in good health".

"The health and well-being of the child was paramount. We contacted paramedics and police straight away and full inquiries are now being undertaken," Mr Grundy said.

Mr Grundy would not comment as to whether this kind of incident had happened before, stating that as the current situation was under investigation, he couldn't say much.

According to the Yass Little Learners' website, the child care business is planning to open centres in Mudgee, Lake Cathie and Bruce in Canberra.

A Yass Little Learners father, who asked for anonymity, said the centre's pick-up and drop-off seemed "relaxed".

He said parents were required to sign in using a computer tablet at the desk, but "rarely is there an actual acknowledgement (from a teacher) that you (the parent and child) are coming and going".

"Surely there was a process in place to pick this up?" he asked.

The father said there was a teacher with a clipboard checking off the children who were leaving when he collected his son on Wednesday, the day of the incident.

The father had kept his son at home on Thursday. "Until we understand why they didn't have processes in place to pick this up, then we can't really let him go," he said.

Another father, Mitchell Ballard, said the child care centre was quiet when his partner dropped off their son on Thursday morning.

And a mother, Mel, said she was at home with her two children on Thursday, taking leave from work to find an alternative day care centre. "I just can't send them back after this," she said.

Her oldest daughter had travelled on the child care centre's bus for outings. "It makes me feel sick to think this could have been one of my girls," she said.

Hume Police will report their findings to Family and Community Services (FACS).