Methotrexate use in children

Hi, My son has severe psoriasis which started at 3 years old. There is no family history of psoriasis so it came as a bit of a shock. He was prescribed Dovobet but due to his young age light therapy is not really a viable option. His skin is particularly bad at the moment from scalp down to his feet with few areas unaffected. Last year he went on cyclosporin for 8 weeks which did improve his skin but he grew excess hair on his body (one of the known side effects) and he spent his 4th birthday in hospital with a virus which was more than likely made worse as his immunity was lowered. His consultant has suggested that he now goes on methotrexate. I'm worried as he is so young. Does any one have any experience of using this drug at a young age? I'm wondering how long methotrexate can be used for? I don't want to use the drug now if this will compromise him being able to use it later in life as teenage years may be more difficult for his self esteem.