Sighting J Lance's answer from your previous question "Are photo releases necessary when using event photos in my portfolio?" The same holds true here. If in a public place, the "public" has no right to stop you from publishing work. Guardians of a minor may withhold names out of protection or fear, but you have every right to photograph them.

When I'm shooting for an editorial I simply state who I'm working for and what the story is about (if its not all ready obvious: we're at the county fair. Yup, doing an article on the county fair.) Most parents are stoked that their kid might be in the paper. I always leave them with my contact information so if they have any questions (or want to purchase a print) they can reach me.

To answer more directly:

1. It would be an incomplete caption if your subject is not named and will not be accepted by editorials you might be submitting to.
2. Same thing applies. Without both names most editorials just won't run the artwork.
3. The "opt-out" is either you have their name or the photo doesn't run. This is, in my opinion, one of the hardest aspects of the job. Don't give them an ultimatum; you'll lose. An appeal to their humanity is better. Show them the photo. Get excited. Use the "Sullivan Nod."
4. Best practice is to be friendly, transparent and confident. "Are you so and so's Mom? Oh great! I'm shooting for _____ and I just got the cutest picture of so and so. Check it out!" "Oh that is cute!" "Sure is. Say, to use this I have to fill out caption info. Is it okay if I put so and so's name down?" "Oh of course. Thanks for asking!"

If you want to use the image of the kid for stock sales, then you have to have a release. Any time I get an image "on the street" that I might sell I get the subjects contact info and mailing address with the release so that I can send them a check for 10% of the sale. When this is offered I've never had someone say no. If it sells make sure you do everything in your power to make good on that contract.