K.B.
My daughter was that age when she went to her first movie and she did fine - she's done fine ever since and now she is 4.5. She likes getting popcorn there so it's a real treat for her. I think it just depends on their temperment and their ability to sit still and pay attention for at least most of the time. Keep in mind too that the movie theater is DARK and it gets LOUD. My cousin tried to take her son for the first time when he was 4 and it made him freak out - they had to leave after 15 minutes because he was just too upset.
However, a 1 year old? No way. I've been in those movies where someone brings their 1 year old (18 months, whatever) and all you hear is the mom telling them to come back, sit down, getting up to pick them up, etc. Really takes away from me being able to enjoy the movie that I paid money to go see.