The three littluns are Henry, Percival, and Johnny.
Littleuns are little boys under and around the age of ten.
The undoubted littluns, those aged about six, led a quite distinct, and at the same time intense, life of their own. (ch 4)
The biggest lttileun is Henry. He is a “distant relative” of the “mulberry-marked face” boy who had not been seen since the fire, but not old enough to realize it. The other two boys are younger. Percival is “mousecolored” and was not even attractive to his own mother. Johnny has a “natural belligerence.” At the beginning of chapter 4, the three boys are at peace.
The little boys mostly just eat and play, but when the older boys come over trouble happens. Maurice and Roger stop by, and Roger destroys the sand castles Henry, Percival, and Johnny were building. Percival began to whimper, and Maurice felt bad, but Roger did not care. This demonstrates Roger's personality.