This is incorrect, as pointed out below. In the US, it is basically entirely up to the news organization, and news organizations usually don't hesitate to name minors accused of newsworthy crimes.
Sometimes, as also mentioned below, local newspapers and stations will withold names for low level crimes, but that is at their discretion. Think of a small town "police blotter" page. (I suppose in situations where there was no real crime, police could choose to withold the names of those involved. I also suppose a news organization could FOIA to find out who called the cops to get rid of a bat in their house. But who would bother.)
But if something has "made it" to the attention of the national media, then the minors involved are almost certainly going to be named. If the story is a "light" one (8-year-old arrested for driving on highway! She kept to the speed limit!), then there's a decent chance the kid won't be named.
Additionally, if, say, a crime is being alleged by friends or family, but someone hasn't been accused by the police or in a lawsuit, then some news sources might publish a "blind item" about it, where the names of some or all parties are not published.
Police will also sometimes withold the names of people involved in a crime (victims and alleged perpetrators) for some amount of time to, say, keep them safe, or to inform the family of the victim. It seems like the most commonly witheld category of name is that of an officer involved in a shooting.
What may be confusing you is that news organizations usually withold the names of victims of sexual assault, especially minor victims of sexual assault. This can lead to some somewhat strange things. For example, when the family of the Michael Jackson accuser sued, the boy had previously been broadcast in pieces of video with MJ. The news used those same videos, but blurred the boy's face.
You'll also see some somewhat strange reporting if, say, the alleged perpetrator of the crime is the victim's family. Sometimes the name of the accused will be reported on Monday, when it's unclear who the victim was, then withheld on reports on Tuesday, because naming him or her would essentially name the victim.
But if the victim (or family) announces themselves, then the US media will typically name the victim. If the victim is dead, the media will name the victim.
An aside, in a weird case in Canada, a judge ruled that the name of the victim of an underage sex assault could not be reported on, due to Canada law, after it had been very, very widely reported ( http://www.slate.com/blogs/xx_factor/2014/09/29/rehtaeh_parsons_canadian_journalists_can_t_print_her_name_as_a_suspect_pleads.html).
tl;dr: Not true. In America it's up to the news organization, and names of accused, especially in national stories, are almost always reported. Victims of sexual assault are typically not named.