Absolutely! The more the merrier. We couldn't imagine our day without all the little ones in our lives!
If your invitation says “and Guest,” then yes, if not, we would prefer if it was just you.
Casual, but really whatever makes you feel comfortable! Whether this is your opportunity to pull out that cute dress you've been saving for a special occasion or you're the kind of person who owns one unstained pair of "church jeans", you'll fit in no matter what.