Hirst made his debut for the England Under-17 national team during the Algarve Cup in February 2016 - in his second game for the team he scored twice against Germany in a 2-2 draw. He was subsequently called up to the squad for the 2016 UEFA European Under-17 Championship in Azerbaijan. In the group stage Hirst scored against Denmark and started the Quarter-final defeat against Spain.
On 23 August 2016, Hirst was called up to the England U18's for the first time. In Summer 2017, Hirst represented England Under 20s at the 2017 Toulon Tournament, scoring a hat-trick in a game against Cuba to take his 2016-2017 tally to 40 goals in all competitions. Hirst started in the final against the Ivory Coast which England won on penalties and was subsequently named in the team of the tournament.
On 1 September 2017, Hirst scored his second hat-trick of the Summer in a victory against Poland, for England Under-19.