I can't definitely tell you that lazy eyes can be fixed. But it is possible to straighten lazy eyes with the help of an eye doctors. Also, i heard that strabismus eye surgeon can correct lazy eyes. But you shall consult an eye doctor if strabismus eye surgeon is available for child. Besides, wearing eye patch can help people straighten lazy eyes. And this treatment is widely used to children. You let your child have a try. Anyway, you are suggested to take him to an eye doctor for an completely eye exam so as to get an good treatment according to his eye condition.
In fact, a lazy eye can be improved by wearing eye patch. You shall have your child put a patch over the good eye so as to force the brain to see with the weaker eye. To help the him, you shall have your child wear patch at lest two hours every day. Personally, you can advise him wear eye patch all the time. It is said that a child of five- to seven-years old can fix their lazy eyes by wearing patch. So, just do it!