You will need:
Some cute stationary (we used some with her initial on the front)
A Stamp pad (I got mine at Marshall's for $1.49... love Marshalls!!!)
And one of these!
Just take her little footsie and press it into the stamp pad (I do it when she's sitting in my lap facing outwards) and press onto the card.
Write out a cute note. Sign your little one's name. And voila! A super cute way to say "thank you!"
You can also use this idea to make Valentine's cards from your new baby and enclose a photo of them at this age. I used this idea to put a green footprint in some of her "Christmas cards" to those attending at our home. I figure she's be so much bigger next Christmas.
While I'm writing out thank you's I also write a note to Ava and mark the envelope with her age and place some recent photos inside.
I will put the notes in her baby book, so that when she's older, she can read them and see how much her feet have grown and how much I loved her from the very beginning. Enjoy!