Are there any circumstances under which a minor a boy under the age of thirteen may be counted towards a Minyan? If, for example, nine men are in the synagogue together with an eight-year-old boy who knows how to pray and understands the concept of prayer, may they count him towards the Minyan and thus conduct a regular service?
The Gemara in Masechet Berachot (48a) comments that with regard to the "Zimun" blessing recited before Birkat Ha'mazon, a minor may, strictly speaking, count towards the minimum quorum of three participants to allow the recitation. Rabbenu Tam (France, 1100-1171), as cited by Tosefot, suggested that this ruling should perhaps extend to prayer, as well, and a minor who understands the concept of prayer should perhaps be counted towards a Minyan. In practice, however, Rabbenu Tam did not rely on this theory, and did not allow counting a minor towards a Minyan. Tosefot add that there were those who allowed counting a minor towards a Minyan if he held a Humash in his hand, but Rabbenu Tam rejected this view out of hand, referring to it as a "Minhag Shetut" ("a foolish practice").
As for the final Halacha, the Shulhan Aruch (Orah Haim 55:4) records the view that a child who is at least six years of age and understands the concept of prayer may be counted towards a Minyan. The Shulhan Aruch then adds, however, that the leading Halachic authorities did not accept this view. Thus, even if nine adult males and a child are present, they may not recite the parts of the service requiring a Minyan. Hacham Ovadia Yosef added that if a person finds himself in such a situation, and the others wish to count the child towards a Minyan and conduct a regular service, the individual should leave the synagogue in order to prevent them from this forbidden act.
In the subsequent passage, the Shulhan Aruch defines the term "adult" for the purposes of this Halacha as a boy who has reached thirteen years of age and has grown at least two adolescent hairs. If it is not known whether he has grown adolescent hair, but it is established that he has reached the age of thirteen, he may be counted towards a Minyan on the assumption that he has grown hair. So long as the absence of hair has not been established, a thirteen-year-old boy may be counted towards a Minyan.
Summary: A boy who has yet to reach the age of Bar-Misva may not be counted towards a Minyan under any circumstances; a Minyan, by definition, requires the presence of ten adult males.
