We're happy to be of service! Here are the answers to your questions:
1. There are PhotoPass photographers all over the place. They're usually wearing a vest and they're always holding a camera. You really can't miss them. When a photographer first takes your photo, they will just hand you a PhotoPass card. Even if you already have a card but don't have it at the ready, the photographers will give you additional cards any time. The cards are free. You can then use the code number on the back of the card to look at your pictures online and decide which ones you want to buy. Or, if you're going to want tons of photos, then you can purchase them all on a photo CD.
2. We don't have any insider information, but I think it would be extremely unlikely that the free dining dates would be extended.
3. Le Cellier is absolutely fine for children. Every time I've ever been there, there have been dozens of children in the restaurant. I would NOT cancel your reservation. Disney Mom Darcie answers a similar question
here and came to the same conclusion I did.
I hope you have a wonderful trip!