If anyone reads the medieval history of India, it is clearly seen that the custom of child marriage is a spin off of the Islamic invasions... because of high value was placed on feminine chastity. No Hindu scriptures promoted child marriage. In fact marriage until a girl reaches puberty is "prohibited". Then she was afforded 4 out of 8 types of marriages... which meant choosing a partner herself or marrying a suitor chosen by parents... in which case a girl was offered only to an eligible candidate, who himself did not ask for her hand. Manu Smŗti recognizes eight types of marriages. 1. Brāhma, where gift of a marriageable daughter is made with suitable dowry to a learned man of good conduct who the father or guardian especially invites. This is referred to in the Matsya Purana. 2. In the Daiva form of marriage, gift of a daughter duly bedecked was to a Brahmin officiating at sacrifice, during the course of its performance. 3. The Ārşa form of marriage is one in which an intellectual reluctant to enter the responsibilities of marriage is given a daughter in wedlock. A cow and a bull or two pairs is the fee charged to ensure that the sagely groom has decide to become a householder. 4. The Prajāpatya form of marriage is for the sake of progeny. These are the normal forms of marriage. The Paiśāca and the Āsura form of marriage were considered unlawful even in Manu’s time. Manu Smriti III.34 abducting a damsel was thoroughly condemned: Suptāṁ mattāṁ pramattāṁ vā raho yatropagacchati l Sa pāpişţho vivāhānāṁ paiśācāşţamo’dhamah ll सुप्तां मत्तां प्रमत्तां वा रहो यत्रोपगच्छति l स पापिष्ठो विवाहानां पैशाचाष्टोऽधमः ll Gauna or dviragaman took place 2 years after any type of above four weddings, which was pointless in the remaining four types of weddings: 5. Āsura or undivine: A sort of elopement. Bride’s people being appeased by giving wealth. 6. Gāndharva (romantic or love marriage). 7. The Rākşasa form or abduction. 8. Paiśāca or Devilish form is molestation. The last two being the examples of forced marriages, and were thoroughly condemned According to Matsya Purana (226/128 and 11/53), a girl being free to chose her husband after third menstruation; self-courted husband; given by the parents or guardian kasya bharturaham dattā कस्य भर्तुरहं दत्ता... – it was Brāhma-vivāha. Gāndharva-vivāha, for instance, was when Budha enticed Ilā (105/8). The example of Ārşa-vivāha is Devayāni’s request for marriage made to Kaca: Gŗhāņa pāņiṁ vidhivanmama mantrapuraskŗtam... गृहाण पाणिं विधिवन्मम मंत्रपुरस्कृतम्... (26/5), which was lawful as she was major and free to marry according to the laws and customs prevailing then. So was valid Kaca’s refusal to this Ārşa form of marriage in which an intellectual reluctant to enter the responsibilities of marriage was being asked to do so. Hypergamy, however, was permitted by Dharma Sūtras: each Varņa marrying within and also allowed to marry from those ones below; i.e., the Brāhmin to a Brāhmin, Kaśtriya or Vaiśya; the Kśatriya to either a Kśatriya or a Vaiśya; and a Vaiśya to another Vaiśya or a Śūdra. Manu Smŗti III.5 is in agreement as are various Dharma Sūtras (Āpastamba Dharma Sūtra ii.5,15,16 etc. and Yajñavalkya Dharma Sūtras i.52,53 as quoted by Macdonell and Keath: Vedic Index i. 475) असपिण्डा च या मातुरसगोत्रा च या पितुः l सा प्रशस्ता द्विजातिनां दारकर्मणि मैथुने ll Manu Smŗti III.13, however, under no circumstances permits a Śūdra wife for either a Brāhmin or a Kśatriya. शूद्रैव भार्या शूद्रस्य सा च स्वा विशः स्मृते l ते च स्वा चैव राज्ञस्य ताश्च स्वा चाग्रजन्मनः ll Prohibition of Sagotra and Sapravara marriage is post-Vedic, later than 600 BC; Smritis allow them. परस्परञ्च सम्बंधः सगोत्राणामभूत कथं l वैवाहिक तत्सुतानाञ्छिन्धि मे संशयं विभो ll And Manu Smriti allowed for equality of the gender by providing for a woman to take another husband under specific circumstances.
