Since children can't use NEXUS kiosks (no eye scans) = we always used the Crew/Special lane as family
I guess I still need to fill out a form?

How about when you connect a flight in Canada to an international destination? Do you still need to fill it out then?

Are you using a NEXUS self-serve kiosk? No, so you need to fill out the form.

Are you using a NEXUS self-serve kiosk? If so, no need for a form.

What if you use the kiosks for the adults and use the crew line for the children...

What do you mean? My kids got their eyes scanned (5 and 8). Had the interview last month.

I don't think there is a rule that says kids CAN'T have iris scans, when my kids got their cards at ages 4 & 6, the officials suggested not scanning them so that if, for example, we were arriving back in Canada late at night, it would be easier just going to crew counter rather than trying to get tired kids to scan their irises at the finicky machines. You needed to have the "NO IRIS SCAN" stickers on the back of their cards in order to use the crew lines.

When they got their cards renewed five years later, their irises were scanned with no issues.

I forgot to bring my NEXUS card recently, but was still able to use GE when crossing from US to Canada with having just the number.

Can I do the same when crossing from Canada to US? Or is having the physical nexus card required?

With a US passport, I've only needed the passport and never needed a card to enter the US (assuming air travel) regardless of the country.

There's also no GE going into Canada. Don't think andrewho was referring to air travel as there is no mechanism to activate the NEXUS kiosk without the card. As for land travel, he is lucky they didn't revoke on the spot if he was using a NEXUS lane.

I would never risk going between Canada and the USA in either direction without the card. Remember that NEXUS members cannot concurrently be Global Entry members. They can only use the Global Entry facilities as a benefit of their NEXUS memberships. That means that when a NEXUS member uses the GE facilities, all NEXUS rules apply, including having the card in your possession when using any NEXUS services.

If you choose to ignore these rules and leave the card at home, you do so at your own risk.

Moderator's Note:
 

A recent question about NEXUS applications processing time was moved to the following thread:
TWA884
Travel Safety/Security co-moderator

My kids were 2 and 0 (or 3 and 1?) when they got their cards
Clearly no "reliable" scans possible
Heck, my son's NEXUS photo is of him CRYING and few agents have commented on it jokingly (never had issue)

They're older now so when they renew they can probably do IRIS scans then

They also didn't have fingerprints for Global Entry either, so we always did GE like this - 2 Adults x GE and 2 Kids GE (but forms with big X spit out immediately), then visit CREW lane again

Seems pretty self-explanitory...the parents using the kiosk's don't need a form, and the kid seeing the agent does.

Our experience going to Canada is we all use the crew line since the kid needs to anyway. Once, the officer told us that we needed to use the kiosk for the adults, and so we went back to do it, and then she processed child. That time, she was busy doing some other work...so I think she just wanted to make it easier on herself. US-bound, we all use the machine, with the child getting the X and we go to the person. Bonus of this method is we still don't have to wait in GE line, but are more likely to bring food in since we have to see the officer anyway, and it's typically cleared right there without a need for secondary.

Moderator's Note:
 

A recent question about using the NEXUS line before the card arrives was moved to the following thread:
TWA884
Travel Safety/Security co-moderator

I am a Canadian citizen with NEXUS and I'll be travelling to the US in the next couple days. However, I am applying for a visa (foreign country, not US) so I plan to travel WITHOUT my Canadian passport.

From YYZ, I will fly UA and then 3 other domestic US flights on UA (I guess I could use a drivers lic, or NEXUS), and then AC to fly back to Canada.
Is this an issue with airline GAs? It appears that CBP and CBSA are fine for using NEXUS as ID, proof of citizenship, entry document, etc. But a bunch of other forum threads have mentioned problems with GAs.

Should I have any concerns? Otherwise I will have to bring my passport and pay extra for rush/expedited visa application.