Boss of the League One side Joe Dunne has moved quickly to agree to three-month loan deals for the promising young players, who have impressed for the reserves so far this season.
The 21-year-olds have both tasted first-team football at the Emirates Stadium in the past, and both have played important roles in the reserves so far this season.
Watt, a former England Under-19 striker, has scored four goals in four games for the Gunners' second string this campaign, and he has been sent on several similar loan deals in the past, spending time at Leeds, Sheffield Wednesday, Crawley and Southend over the last two seasons.
Eastmond, a midfielder who played 14 games for Wycombe Wanderers last season, has represented Arsene Wenger's first team on 10 occasions, including a UEFA Champions League fixture away to Shakhtar Donetsk.
Both players were involved in Arsenal's pre-season tour of Asia this summer, where they faced a Malaysian XI, Manchester City and Kitchee. Watt and Eastmond are new Colchester boss Joe Dunne's second and third loan signings since taking over from John Ward on Thursday, with MK Dons striker Jabo Ibehre also bolstering the ranks for the struggling League One side.
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