Reaching

My 4 month old doesn't reach for or bat at her toys. Even when I put her on her activity mat she just watches the movement and colors and makes no attempt to reach or touch anything - should I be concerned? She follows toys I dangle in front of her with her eyes and they make her laugh and if I put something in her lap she will grasp it (accidentally?) and bring it to her mouth. She's always sucking on her fingers, too. She's very social and has rolled a few times, this just seems like a milestone she is going to be slow to hit. She was born 3 weeks early so I'm not sure if that makes a difference?