Child understanding baptism

Here is my issue, and I don't think I would even call it an issue.

My son, who is almost 6, came to me several months ago and told me he had ask Jesus into his heart. He told me this two days in a row. I did not want to make a really big deal out of this in front of him and wanted to know if it was real or if it was a "my friends did it" situation.

As time has gone by, I'll drop little hints here and there about it without him knowing. Like at bed time when we say our prayers.
"Hey buddy, what do it mean to have Jesus in your heart?" or "If Jesus is in you, how are you to act and where will you go when you die?"
He gives all the correct answers evertime. I'll wait days, if not weeks before asking again.

Now, the issue is baptism. He never really understood what it meant to be baptized. I told him and he has acked like he understands. I ask him about it and he gets the drift of it.

My son and my wife went and talked to the childrens pastor the other day, and he went of the plan of salvation with him again and he nailed everything, even went back and said a prayer for salvation, but was lost on the baptism.

So my overall question is, I know baptism doesn't save you. Faith in Christ alone saves you. Baptism should be your first public act of showing your salvation. With so much being taught about the importance of salvation and accepting Christ in your heart in the childrens minister, it's like baptism is a next step, almost a by product of accepting Christ. They are not really told what baptism is until after they come forward. Where as adults are told about it usually in the same breathe of asking if they accept Christ.

So, would you have an issue with baptizing a child if they don't fully understand or completly grasp the concept baptism if they have said they have accepted Christ?

My boy is my oldest, so I'm only 5 1/2 yrs into this parent thing, so some advice would help. Oh yeah, and two daughters 4 and 3, and a newborn son that's 6 weeks old.

Thanks