Yes. They just need to have an adult on the account with them, usually mom or dad, but it can be a grandparent, aunt, uncle, or other adult. This kind of account is called a custodial account. The kid or teen (referred to as the minor) owns the stock, while the adult (the custodian) has legal responsibility for the account.
Kids and teens can set up their own log-in credentials (separate from the adult) so they can see how their stocks are doing anytime they want, without bugging mom or dad. They can also place stock trades with the adult’s consent.
For example, if a teen wants to buy $20 of Facebook stock, he sets up the transaction, which is routed by email to mom for approval. If mom approves, the trade goes to market and executes.