Wow you're a nice parent, good for you, I am sure your kids will love them. To answer your questions:
1) I believe ps+ will only transfer to two Vitas, but I may be incorrect
2) I believe it may only apply to two as well since on the disclamer for some games at least it states that the games are able to be transfered over to two systems either portable or console.
3) I believe only one account can be linked with the Vita since the 1.80 update.
4) Yes it does connect via Ad-Hoc, but some games may not allow that option, but for the most part yes.
5) Lego Batman is a port of the 3DS and from what I've heard pretty disappointing, but for kids i believe they will love anything with Batman. BlackOPsD is sort of short on the single player side but I'm enjoying it.
6) A bundle is you're best bet regardless of whether you want BO2 because you literally get afree game and a free memory card, plus the $50 off on the original price.
7) For games for kids I recommend Little Big Planet Vita, Gravity Rush, Need for Speed Mod Nation Racers, and PS+ is a no brainer for new Vita owners.
Now anyone from the community feel free to correct me if I'm wrong on any of the points. Cheers.
just that ps+ only works if its the same account. however, you can probably download to ps3, and try to transfer it to the vita from ps3 through content manager.
most of the other stuff is right (not 100% about crossbuy though)
also, if your looking to get a bundle, the ac3 bundle might be a good deal, but A) ac3L might be to old for kids, and B) if your not going to buy each 1, 2 are gonna think you like the 3rd the best cause he/she got a white vita.
Sony needs to get with the times and allow some kind of family deal and account, it's ridiculous. It's this type of restriction that turns people away from buying one.
I am in a similiar boat as you. I have a ps vita, and both my kids do as well (5 and 10). I bought mine on release day from amazon, but theirs I bought off of craigslist for much better deals (8 games, a 4GB card for each, case for each all for 425 total). So if you miss out on a new one, used might not be a bad place to look.
now back on topic, with 3 Vitas in the house, and I already having plus we need to figure out
1) are plus games tied to one acct?
2) sub accounts can get plus, but as per their ToS the person has to be 18.
3) can plus games be moved over on the ps3 to the sub accounts? (psp games will not move)
A few other things you may like to know is if you child is under 13 some features in near and other options are turned off. They are able to chat without a hitch though.
If i find anything else tonight when the store updates I will try to remember to post here