In the daily practice of Jewish life it is a well-known fact that community prayer or Torah reading requires a minyan, a quorum of ten Jewish males above the age of Bar Mitzvah.  Although the Gemora (Berachos 47B) discusses the possibility of counting a minor as part of a minyan, the halachic ruling of most poskim is opposed to this. 

R. Yosef Caro, the author of the Shulchan Aruch in his earlier comprehensive vast work, Bais Yosef, cites many opinions in regard to this situation and in the Shulchan Aruch (Orach Chaim, 55,4) he clearly rules against such a practice. 

R’ama even adds that even with “katan” holding a Chumash he should not be counted unless it is a “shaas hadchak” a difficult situation.  However in practice many other later poskim rejected the ruling of counting the minor under any circumstances. 

Many American rabbis in various communities were faced with the problem of bringing together a minyan and some felt the need to rely on the lesser opinion.  

However it has been pointed out that this leniency should only be used where the community does not have ten qualified males at all, but if there are a large number who neglect to come to a minyan then the minor should not be counted since the members of the community are obligated to participate with full cooperation.  (see Tshuvos Yaskil Avdi V)  See also Kav Hachaim Orach Chaim 55.