We just finished up a fun week of Gingerbread activities. This was our alphabet activity. I got this idea from here: http://www.pre-kpages.com/gingerbread/. She had a free download of the pages, but it only had letters A-F, so I quickly made some of my own. You can download them here.
To prep this activity, I created the pages, printed them, then laminated pages and letters so they will hold up from year to year.
For my older children (4 and 6), I simply gave the child all of the gingerbread men pages and all of the letters (upper and lowercase) at the same time and told them to match them up. They put the upper and lowercase letters on the same man. This is something that helps them work on letter recognition and keeps them occupied for a good chunk of time. They don't need any assistance from you.
For my 2.5 year old, we did things differently. We did one sheet at a time. I gave her the upper and lowercase letters for the letters on that sheet. She could do the uppercase all by herself, so if you want a younger child to do this activity independently, you might want to just do uppercase letters. She needed help with the lowercase letters.
The way I helped her understand grouping the letters together even if they looked different is I told her the man on the page is the "daddy letter," the uppercase letter was the "mommy letter," and the lowercase letter was a "baby letter." This worked for her because she is obsessed with babies. It helped her grasp that the letters can go together even if they don't look the exact same.
I had her hold a letter up and tell me what letter it was, then match it. She could get all uppercase, and knew some lowercase, but didn't know them all. It was a great exercise in getting her to think about lowercase letters.
For younger toddlers, I would recommend doing just uppercase. For a pre-toddler or baby, you might hold the letter up and say what it is and then put it on the page or have your child put it on the page if possible.