I've been following this case the past few days. The mother disappeared with her son in the hope of preventing him receiving radiotherapy treatment recommended by his doctors. They had already removed his tumour, and the additional radiotherapy is proven to increase survival rates in affected children to an 80% success rate. The mother believes in complimentary therapies, as many people do, and stated in earlier interviews she had researched the condition on the Internet and was worried about the possible side effects affecting her son in the long term.
Personally I would want my child to be alive with unwanted side effects, rather than run the risk of delaying radiotherapy until the cancer definitely returns and maybe being too late for treatment to be effective.