The site of the old Royal Children's Hospital has been returned to the 170-hectare Royal Park. The $5.5 million new section of the park completes a $1 billion project to build a new children's hospital on Flemington Road, which began in 2005.

Giant slides and an adventure playground were enthusiastically tested by children from the hospital and local schools on Wednesday morning.

The new parkland includes more than 1100 trees and 17,500 other plants and grasses.

Indigenous history has also been incorporated into the design, which has a large grassy hill overlooking the playground.

The children and their parents were joined by Premier Daniel Andrews, ministers Jill Hennessy and Lisa Neville, and lord mayor Robert Doyle for the opening.

"This precinct is just a magical space of healing and love and care and now a wonderful park for our kids," Mr Andrews said.

He said the park would entertain patients and children visiting the hospital as well as children from across the city.

Cr Doyle said one of Melbourne's great parks now had one of the city's great playgrounds.

The previous Labor's government's pledge that the new hospital would not use more than 4.1 hectares of Royal Park has also been met.