What I have done in the past
Gotten plaid fabric ribbion, maybe a yard of it or so ,thumb tack it to the doorway.
then as the cards come in I take craft glue and dot it to the card and press on the ribbion. I have also used straight pins
and one year I took the squeeze clothespins painted them,glued them to the fabric and then clipped the cards . its easy,cheap and something kids could do . I have given them makers and let them go with the clothes pins in red,green,yellow,blue. then I glue the backs to the clothes pins and they press,we hang when dry. Kids are proud.
remember the smile