As far as I understand, as per the explanation to Section 64(1A), the income of the minor child shall be included:
(a) where the marriage of his parents subsists, in the income of that parent whose total income (excluding the income includible under this sub-section) is greater; or
(b) where the marriage of his parents does not subsist, in the income of that parent who maintains the minor child in the previous year.
Since in the instant case aforementioned clause (a) will apply and thus, the income of minor child shall be clubbed in the income of the parent having higher income i.e. Father.
Also, Assessing Officer has a right to make rectifications in the ITR of mother and father as the current treatment is not in line with tax provisions.