M.P.
I'm with the halloween card person (although I'd try to find a more recent picture and send it before halloween cuz that's still 2 months away) and think you should send a "thanks again" photo card.
Why don't you send a photo from the baptism instead of a halloween card?
Honestly I think thank yous are important but they are also over-rated. If the people who gave you the gifts really care about you they'll know you appreciate the gifts without the formality of a card and they'll understand you have a new baby and you're just busy or flakey or whatever new babies make moms. A good person wouldn't hold a late or absent thank you card against you.
I have to wonder what kind of people really have the time and energy and desire to sit around waiting for thank you cards for things they bought. Unless what they gave was a couple thousand dollar bond or a home-made gift that took weeks to make, they really should find something else to do with their time. This isn't a birthday thank you we're talking about, it's a baptism thank you. Obviously the baby is new and you're busy as heck. A good person won't hold it against you.