Need to Declare

I'm wondering if I will be stopped or checked extensively if I declared I brought certain items into Japan? Will this cause a great delay as I intend to connect to a domestic flight and wouldn't want to be caught at customs for ages.

Among the things I am bringing are baby milk (I have a 1+ year old), medication for baby and child, some snacks since I am not sure if they are available in Japan or easy to find.

Rgds.

No, unless you are carrying something that is a restricted item, declaring things will have little to no effect on how fast you get through customs. Most of the stuff that you've listed you wouldn't have to declare anyway. Btw, what type of medication? Some things that are over the counter in your country may be prescription in Japan, so you may want to check on that.

The usual medication for children travelling like for colds/flu,cough,travel sickness. They are over the counter.

The usual medication for children travelling like for colds/flu,cough,travel sickness. They are over the counter.

Check to see if they contain decongestants like pseudoephedrine. If so you won't be able to bring them without a prescription.

I hope they are not that thorough to scrutinise everything.

Generally no, but getting caught in possession of controlled substances is never a good idea, especially when travelling in a foreign country. It's fairly easy situation to avoid though, just get alternative medications that don't have controlled substances in them.