Alphabet Hunt and Match

My kids love to look for things, so we set out to look for the alphabet.

I got some alphabet flash cards from the dollar store and wanted to find a fun way to use them.  So I made this from construction paper and wrapping paper:

And hid these:

And set the kids to finding and matching.  (I could have just bought two packs of cards and taped one set down, but I wanted them to match the letters and not the pictures.)

I realize now that I shouldn't have done the whole alphabet because Drew didn't even want to try to match them at first.  Then I started pointing out letters he knows (like the ones in his name) and he got into it a little more.  After that, I told him what row the letter was in.  We got about halfway through because a certain two year old was determined to keep messing up the cards by doing this:

After that, he was done and I didn't push it.  To be honest, I was done too.  But I think I'll try this again with fewer letters.

Any tips for keeping kids interested in learning letters?