Relationship proof for a child

Hi,

I'm non-Japanese national planning a short trip to Japan with my 7-yrs old son.

He is on his own international passport and we all have valid visas. However, I worry a bit about having no formal evidence of a relationship between us (there is no parent's record in passports in my country). I take his original birth certificate with me (and made an English translation of it just in case); will it be enough to enter Japan?

I have no idea what an "international passport" is, but I don't think a proof of relationship is normally required as a condition for entering Japan.

I've entered Japan more than a dozen times (Australian passports) over the last five years with my child- we both have different surnames- it's never ever been an issue- never once has immigration even batted an eyelid. I'm sure it will be fine.

Thanks for replies, everybody. This isn't my first trip to Japan (or my first trip with the son), but I've heard some rumours and wanted to clarify the situation.

As for "international passport", that's what you normally call a "passport" in the majority of countries. :-) Some of us still have a local passport and an internationally recognized one.