Let me begin by saying we didn't take our kids until the youngest was 5. I was a SAHM for a few years, and we simply couldn't afford it.
So, as always, take my advice for what it's worth, but here it is:
There's so much information out there-- so many choices, so much to do, so many things you can do to add a little "extra" to your WDW vacation.
And the reality is that your kids are going to have a fabulous time without any of those extras. So keep your eye on the big picture-- your 6 year old son and the things you can do to help him really enjoy his trip. You may find that the monorail is his favorite ride--- great, do a loop each day. You may find that Indy Speedway does the trick-- great, change your fastpasses so he gets to do it more than once.
You'll want to sign up for a "fairy godmailer" here:
http://www.disboards.com/threads/fairy-godmailer-list-part-ii-aka-fgm.2440121/ Someone going to WDW before you will send a postcard from the characters, anticipating your stay, and you pay it forward by doing the same thing for someone while you're there. Your kids will be charmed.
And you know he'll want some quality time in the resort pool. Even if you have a pool at home.
But you'll find lots of things that will enable you to spend a fortune if you want. And, yes, your kids will enjoy them. But no more than the vacation you would have planned if you and they had never heard of the pirate cruise or the arcade or the fireworks cruise or all those extras.
You may also find that either or both of your kids are fine with the idea of characters, but they're terrified up close and personal. OK, great, adjust your ADRs to avoid the characters.
Too many people get so caught up in seeing it all, doing it all, getting the most bang for their buck that they forget that this is about a family vacation. It's all about spending time together, enjoying WDW and each other.