no board is good or bad. the child's ability to cope with it matters most. please do not think about competitive exams at this stage of life. check out syllabus of both boards and properly evaluate where your child will excel.
I personally feel the ICSE syllabus gives well rounded education, your son will really get educated. But it's true that CBSE syllabus helps more for competitive exams, so if you want your son to get into engineering or medical then yes go for CBSE, for all other avenues in life its better to opt for ICSE.