"There are no plans to expand the current services in the short term," a spokesperson told RNZ.
A mobile X-ray machine has been donated by the Wellington Hospital Foundation. Other types of radiology are much more expensive.
Public hospital clinical services nationwide are short of staff and under high pressure.
"We may add services or resources in the future based on changes in how we provide care, or across the wider hospital network," the hospital said.
The existing services would be closer at hand to the children's hospital and so care would be better co-ordinated "and better support health outcomes for young people", it told RNZ.
Level three has a bridge connected to the rest of the hospital.
Ward rooms would be larger, have their own ensuites, and a pulldown bed for parents to stay.
The opening is a key step to activating a plan to move many services, including getting the Emergency Department out of a quake-prone building, in a series of rapid shifts as part of a redevelopment worth up to $2 billion.