Its really difficult to explain divorce to a small kid but the best way would be explaining him in his way. You should take a friendly approach while explaining and please never blame your spouse for this as this will create negativity in the mind of the child. You can explain him by saying just like there is a fight between friends, similarly there is fight between papa and mumma. As a result of fight, they will be living spearately but bothe will be there for you and will love you as before. With these kind of explanation, your child will feel at ease and will not withdraw into a shell.
Hi... you are right. We as a parents have responsibility towards our kids. such an important issue needs sensitive handling. Any insensitivity can lead to developmental problems in kids. Parents must explain the child about this issue together so that the child gets the feeling that his parents are together and doing the right thing. Gradually, he can be explained why they need to live separately. To a 6 yr old kid, it is best not to divulge too much details as they can be harsh on him.