2010-11: Aaron Haydon attended USA Hockey's Select 14 Festival in July before skating for the Belle Tire '96 bantam team that captured the 2011 U14 national championship.
2011-12: Haydon participated in USA Hockey's Select 15 Development Camp and skated for Belle Tire's midget major U16 team. In 40 regular season games he scored 2 goal with 9 assists and 93 penalty minutes. He scored 3 goals with 3 assists and had 28 penalty minutes in seven playoff games. Haydon was selected by Niagara in the first round (20th overall) of the 2012 OHL Priority Draft.
2012-13: Haydon made the jump directly from midget minor hockey to major junior; skating for the OHL's Niagara IceDogs as a 16-year-old. He played 42 regular season games — scoring 4 goals with 6 assists — and was -7 with 39 penalty minutes. Niagara finished fourth in the Central Division and lost to Oshawa in a first round playoff series. Haydon appeared in three playoff games and was -1 with 1 assist and 2 penalty minutes.
2013-14: Haydon returned to Niagara for his second OHL season after skating for the USA U18 team at the 2013 Ivan Hlinka Memorial Tournament in August. He had no points and was +1 with 10 penalty minutes in five games for the USA at the Ivan Hlinka Tournament. Haydon was named to the 2013 CCM/USA All-American Prospects Game and selected to Team Orr for the 2014 BMO CHL/NHL Top Prospects Game.