In a perfect world
You can be there for your favorite cousin's nuptials and show off the baby to extended family members. The invite didn't say "Kids Welcome," but who wouldn't be thrilled to see little Emma in her adorable dress?
If kids aren't invited, don't bring them. Period. If you don't know whether they are, ask before you RSVP.
Go without your baby. Some brides and grooms set up free on-site babysitting, usually in a room at the hotel or reception hall so you can dash off to nurse or cuddle your infant in between "The Chicken Dance" and "Hot Hot Hot." If that's not the case, the bride may be able to steer you toward other guests who have little kids and might be happy to share a sitter with you.