It's not wrong if you put it, but it slightly changes the meaning. "Ele é o meu filho" feels more like "This is my son". The point is that without the article "meu filho" kinda works like an adjective, qualifying "Ele". When you put the article it works like a noun, like it's talking about a specific person (maybe someone they talked about earlier). It's a bit difficult to explain since I don't think you have this distinction in English.
It really depends on the person's accent.
The are accents where "e" and "é" can have the exact same pronunciation when you just mean the letter "e" (as in the alphabet), but it can have another pronunciation when it is the "e" meaning "and". While for other accents the pronunciation is the same for both cases.
Check out the first three pronunciations in this site.
- The first one is how "é" sounds (it sounds like that for every accent) - but some accents pronounce the "e" like that too.
- The third one is how "ê" sounds (again, same for every accent) - but some accents pronounce the "e" like that too.
- The second one is how some accents pronounce the "e" in a sentence (either when it means "and" or when the "e" is part of a word). The main thing here is that the letter "e" itself is never pronounced like this in Brazil, but it does sound like this when the letter isn't by itself.
It's definitely a little bit tricky! C: