In the United States, many venues that host Metallica concerts do have age restrictions in place. For example, the Madison Square Garden in New York City has a general age restriction of 16 or older for concerts, unless otherwise noted. The Prudential Center in Newark, New Jersey, also typically has a 16 or older age restriction for concerts, although some events may allow children under 16 accompanied by an adult.
It's worth noting that even if a venue allows children under 12 to attend, the concert environment may not be suitable for young children. Metallica's concerts are known for being loud and intense, and the mosh pits and crowds can be quite rowdy. Therefore, it's important to carefully consider whether your child would be comfortable and safe in such an environment before deciding to take them to a concert.
If you do decide to take your child to a Metallica concert, it's a good idea to prepare them for what they might experience. Talk to them about the loud music, the crowds, and the potential for moshing and other rowdy behavior. Make sure they understand that they can always come to you if they feel overwhelmed or uncomfortable.