Our son suffers from eczema behind his joints. Often it causes him pain and he is unable to move his legs. On Shabbos, would we be able to dab on Vaseline or cream with a spoon (without rubbing anything in). Not using Vaseline or cream would mean him not being able to get out of bed.
The Vaseline should not be rubbed in (this would constitute a problem of memare’ach), but it can be dubbed onto the area without rubbing it in.
This will not involve a problem of refu’ah, in particular if not using the Vaseline would leave your son bedridden.
Good luck and good Shabbos.