The adequacy of the Hajj pilgrimage performed by a child is a challenging jurisprudential issue, assuming that his maturity takes place in one of the wugufs, because until the 6^th century AH, Imamiyyah jurists were certain claimants of the adequacy of the Hajj pilgrimage performed by a child, assuming that he got maturity before reaching one of the wuqufs. However, the first figure who doubted the fatwa was Mohaqiq Helli. Fayz Kashani, one of the jurists in the 11^th century AH, basically denies the adequacy of this pilgrimage. The reason for deviating from certain claims to denial in jurisprudential periods is made clear by doing the genealogy of this fatwa, and analyzing the stages of its evolution and the arguments cited in each period. This descriptive-analytical research explains those documents and arguments that reject the adequacy of this pilgrimage. The research also reviews the Imamiyyah jurisprudential works to do the genealogy and discuss the quality of the evolution of the fatwa over many centuries to find out the reasons for differences of opinions. According to this research, the most important reason for differences is the refining and generalizing of the reason for the percept, done by the predecessors, from the Hajj pilgrimage performed by a mature man to the Hajj pilgrimage performed by an immature child. But later on, it was gradually questioned and finally denied. Since there is no plausible reason for proving the adequacy of the Hajj pilgrimage performed by an immature child in the aforementioned case, its inadequacy is acceptable.