Malcolm Sargent House in Prestwick, Ayrshire was targeted in January last year.
Thieves made off with lead from the roof of the home, run by cancer charity CLIC Sargent, causing around £40,000-worth of damage.
The playroom was badly water-damaged and dozens of toys had to be thrown away, but people from the local community and further afield stepped in to help with the refurbishment, the charity said.
Alex Salmond officially reopened the repaired playroom at the home which provides free holidays and short breaks for young people with cancer.
"Like everyone in this community, I was extremely saddened to hear about the mindless act of vandalism and theft that caused great damage to Malcolm Sargent House last year. However, I am delighted to see that something good has come from that incident with this magnificent new playroom for the young people who visit here," Mr Salmond said.
"I am really impressed by the hard work and dedicated efforts of all the staff, volunteers and the community who have rallied around CLIC Sargent in its hour of need and enabled this wonderful playroom to be built.
"I am sure that the families who benefit from this new facility will join with me in acknowledging the tremendous support and assistance CLIC Sargent brings to them."
No arrests have been made in connection with the theft. Inquiries are continuing, a Strathclyde Police spokeswoman said.