That's an excellent question, and a frequently asked one. Like you said, there are several angles or issues involved. I'm no expert on this, but as this had been a concern of mine too I had researched the issue and talked to several pediatricians and electronics experts about it, and this is what I understand:
- Radiation coming from computers is negligible. If it is harmful to a baby, then it's also harmful to you and you would find many people telling YOU to stay away from computers, not just your baby. One point that isn't mentioned much though relates to 'positive ions.' Unlike what it sounds like, POSITIVE ions are actually bad, and NEGATIVE ions are good. (Do a search on negative ions and you will see the difference.) Now, the old CRT (cathode ray tube) monitors, you know, those big bulky ones, do emit a lot of positive ions. People who are particularly sensitive to positive/negative ions (estimated to be about 20% of population) tend to get certain ill effects from prolonged exposure to it, like lower immune systems, moodiness, etc. Thankfully, more and more people nowadays use LCD monitors, which does not have this problem. And as for TV, where there are still many CRT TVs in use, the important thing to do is to keep a distance from it, and minimize the time spent in front of it.
- EYE STRAIN
This is a common cause of complaint, for children and adults alike. I think the seriousness of the problem here depends on the monitor, and in particular, on its refresh rate. Old monitors (especially the CRT ones) have very low refresh rates - if you look closely at these old monitors, you will see the screen flickering. Over time, this tends to cause eye strain. Again, thankfully, modern monitors have very high refresh rates and this problem has been reduced considerably. Many people I know who used to have eye strain problems with old CRT screens no longer have problems with modern-day LCD/plasma screens.
One final note here is glare - make sure the lighting is adequate!
- TV MAKES YOUR BABY STUPID?
Actually, when most people talk about the problems with watching TV, they are actually referring more to this aspect of it. This question is so important that our editor has done a piece on it, which you can read here:http://www.brillbaby.com/teaching/faqsTV.php
In a nutshell - make sure you accompany your baby as much as you can for all TV/computer-watching so that you have stimulation coming from you and not just the TV, and try your best to make the entire process interactive - encourage your baby to respond, ask your baby/child questions (even if they can't talk yet), etc., instead of letting it be purely a one-way process where your baby just stares at the screen for long periods without needing to think or respond.
Hope that helps!