Cole and Pappoe, were both previously at Chelsea, have been with the side throuhgout pre-season and featured in the sides trip to La Manga, Spain.
Under-21 coach Simon Ireland said: “Trial periods are always high pressure for a player because you are on a limited timescale to show what you can do, but both Danny and George have slipped seamlessly into the group and that has paid dividends on and off the pitch.
“We don’t just sign these players on what they do during their trial though, we have looked at both before they came here and we have also looked at what they can offer going forward, and we are very pleased to add them into our squad.
“Both have good experience having played at a club of Chelsea’s stature and we feel they will help us be competitive and provide some stability during our first season as a category one side.
“With so many players taking the step up to the first team recently there has been a void in our under-21s that our under-18s have been filling, but we needed to bring in more faces at under-21 level so that we don’t over exert our youngsters too early.”
Cole, 19, is an attacking midfielder who rose to prominence in Chelsea’s under-18s before leaving Blues at the end of last season.
Central defender Pappoe, 20, has represented Ghana at under-20 level and has already made his professional league debut while briefly on loan at Colchester United in 2013.