Found this in their brochure :
Car parking
There is limited car parking in and around the hospital, so we
advise you, if possible, to use public transport or arrange to be
dropped off at the hospital by car. Many streets are permitonly
zones. Sciennes Road has ticket machines in operation.
If you do bring a car, there are a limited number of car parking spaces
available in Rillbank Terrace for use by parents of children coming to
hospital. Spaces numbered 19-23 are set aside for the use of parents
accompanying children to the Accident and Emergency (A&E)
Department only. The rest are available on a first come, first served basis.
Finding a parking space can be difficult and, if possible, it is advisable
to allow extra time for this. Although there is car park security
surveillance, please ensure that you lock your car and leave valuables
out of sight.
As you can see it is quite difficult. If you are visiting it might be easier to use public transport or have somebody drop you off