Shulchan Arukh Orach Chayim · Siman 596

English

After the (Musaf) Prayer, we trumpet a big teruah blast without a tekiah blast. Rema: There are places that we are accustomed to go back (after the Musaf Prayer) and blast 30 sounds (Minhagim Yishaynim) and after one fulfills these, further there is not to blow more for no reason. But a minor, even one who has reached the Halachic age of maturity, it is allowed to say to him that he should blow the shofar (The Maggid Chapter 2 from the Laws of Shofar). And it is permitted (for a minor) to blow shofar all day (Or Zarua of Rosh HaShana).