Children are a gift from God and He cares about how they are raised (Psalm 127:3; Psalm 34:11; Proverbs 23:13-14). When God gives us gifts, He also gives clear instructions about their use.
When God led the Israelites out of bondage, He commanded them to teach their children all He had done for them (Deuteronomy 6:6-7; 11:19). He desired that the generations to come would continue to uphold all His commands. When one generation fails to instill God’s laws in the next, a society quickly declines. Parents have not only a responsibility to their children, but an assignment from God to impart His values and truth into their lives.
It's imperative that parents control what their children are watching/doing (especially the early years), on any screen, because most of the content on those screens focus on the worst that mankind has to offer and evil is glorified as good (see 2 Timothy 3:1-5; Isaiah 5:20). With unfettered access to TV and all the other devices, a child will grow up learning the values of this world, instead of the values of God.