Mommy, look what I found!

Last week when I picked up Kelsi at the gym's daycare, she was sitting in her car seat sucking her thumb! I thought "When did you find that?". Today, I caught Kelsi doing it again while she was going to sleep in her swing for her afternoon nap. By the way, am I ruining my child by letting her nap in the swing as opposed to putting her in her bed? She doesn't have any problems sleeping at night (still about 10 hours), but the only time she is in her crib is at bedtime. I ask because my friend Amanda who watches her in the morning tried to put her "down" for her morning nap instead of in the swing and she threw a fit. She put her in the swing and she went right to sleep. Thoughts?