I think its their choice. Blood isnt even bad. We need it to live. They may actually learn. For example they may have never known that there was blood in there body. So they stab someone in a game. And there you have it, they learned. . . . .
No, I do not mean blood spewing out like a waterfall, I mean realistically (ex. A bit of blood after scraping your knee) Blood is part of the human body so it shouldn't be hidden if handled correctly. Technically if you shield a child from seeing a bit of blood, you keep them from seeing how scraping your knee, or getting injured really happens.
In conclusion, blood should be subtle but apparent in children's media since it would do no harm and make the media more realistic.