Traveling with two passports: noob question

[poodlek]

I'll be going back to Canada for a visit in a few weeks with my infant son. He has both Canadian and American citizenship, but his immigration status here in Singapore is through his Canadian passport. We'll be traveling through ATL on the way, so my question is since we're going through the USA should I show his American passport, or Canadian since we're starting our trip with it in Singapore, or both or what? What's the typical procedure for someone with dual citizenship? I don't want to be accused of trying to be sneaky, and we all know ignorance doesn't fly as an excuse with the USCBP

[sundaymorningstaple]

My kids have always left Singapore on their Singapore Passports and entered the US on their US passports. Same on the reverse, leave the US on US passport and enter Singapore on Singapore passport. In your case, he would have to leave on his Canadian Passport. As far as entry in the US is concerned, if you are just transiting, makes no real difference, but if you are stay a couple of days, then he should come in on his US passport and leave using the same. Entry into Canada is via Canadian passport.