Hi Rachel,
I think it's good that you are asking this question. There is a ton of literature on it and some people would tell you yes, there is a huge problem with it for children. The rapid change of images (the screens change every few seconds)can affect a child's brain development and some research has shown this to be the cause of the dramatic rise in autism, add, adhd etc. Also, when a child is watching an action on T.V. there is a response in his muscles, however he doesn't actually move his muscles, then later when the T.V. is turned off there is all of this pent up energy and you will notice that chldren often get wild after watching T.V. So it's not even the content that matters as I know there are very wonderful, educational shows on T.V., it's the effect of the rapid movement of the screens that have an effect on the developing brain. There are school movements like Waldorf that don't allow any T.V. at all.
We've been told that for my son especially it is crucial not to have him watch T.V. At first it was difficult but now I LOVE it and I much rather see him building and playing and doing art then watching T.V. As I said there are many books on it you may want to read...trust your intuition that you even came up with this question, not every mom does. Best, C.