After some [light] soul-searching, I decided to inform Amazon so that this new mother could get her gift. Here is my exchange with them:
Me:
hello -- i received an amazon gift card not meant for me. the amount is $100 so i feel bad just adding it to my account. can you contact the seller? can anything be done about this from your end?
Amazon:
Hello,
I'm so sorry for this delivery mix-up.You weren't charged for anything you didn't order.
Please send the information listed below, and we'll try to deactivate the giftcard:
1. Gift card claim code or Gift Card number:
2. Street address or e-mail address where gift card was sent:
3. Name and e-mail address of the sender:
4. Order number (if possible):
Me:
--requested info for #1 and #2
Amazon:
Hello,
Thank you for providing us with the information. We were able to locate the gift card.
Would you like us to:
1. Resend the gift card along with its claim code.
2. Redeem it to your account.
Me:
I would like you to contact the sender. Like I said in my first email, I don't know this person and I don't have a way of getting in touch with them and I feel guilty simply taking the money when it seems to have been sent by accident to the wrong email address.
Amazon:
Hello,
I'm sorry a packing slip wasn't included for you to identify the sender of this gift. Here's the information that would've been on the packing slip:
Sender's Name: [redacted]
Gift Message: [mostly redacted]
Love,
Uncle Jim and Aunt Ginny
Unfortunately, for security reasons I am unable to give you any personal details or information regarding the gift sender.
I hope you enjoy your gift! We look forward to seeing you again soon.
Conclusion? I guess I will enjoy the gift.