The boy, who was collected from home, was on the way to childcare when it is alleged he was left in the unattended vehicle on a day when temperatures in Yass reached 28 degrees.

No charges have been laid and the Yass Little Learners childcare centre is assisting with inquiries, a NSW police spokesman said on Thursday.

Officers were called to the centre just after 3pm when the child was found inside the parked vehicle.

The 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 until 5pm.

In a statement to parents posted on Facebook, Yass Little Learners confirmed the incident and said the driver had been "suspended pending a full investigation by YLL centre management".

The co-owner of the Little Learners Group, Steve Grundy, told The Yass Tribune that the centre was pleased the child was 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 on Wednesday.

The statement assured 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".

Officers from the Hume Police District attended and are conducting inquiries. The matter has been reported to Family and Community Services.

The childcare business, which has been operating in Yass for three years, is planning to open a centre in Bruce, according to its website.

The childcare centre posted on its website in April 2017 to about the then new bus service, which was able to collect children from the town and nearby Murrumbateman.

People with information about the incident have been asked to contact Crime Stoppers on 1800 333 000.