Bhavaprakash purvakhanda bala prakarana 4th chapter 35th sloka:

क्षीरसात्म्यतया क्षीरमाजं गव्यमथापि वा ।

दद्यादास्तन्यपर्याप्तेर्बालेभ्यो वीक्ष्य मात्रया।(भा. प्र. पू. ख. ४/ ३५)

In case of non- availability of breastmilk of dhaatri(wet nurse) or mother, goat's or cow's milk can be given to the child as an alternative, because milk is saatmya(compatible or congenial) food for children.

Shaargadhara samhita poorvakhanda 6th chapter 40th shloka:

क्षीरसात्म्यतयाक्षीरमाजं गव्यमथापि वा।

दद्यादास्तन्य पर्याप्तेर्बालेभ्यो वीक्ष्य मात्रया।

Milk is the saatmya food for the child. Hence in case of non availability of mother's or dhaatri's(wet nurse) milk, goat or cow milk can be given to the child in required quantity.

Charaka samhita:

Acharya Charaka has not mentioned cow or goat milk as an alternative directly. But in many places he mentions that the cow milk as one of the hita food, jeevaneeya food, rasaayana, ojovardhaka.

Sushruta samhita:

क्षीरसात्म्यातया क्षीरमाजं गव्यमथापि च।

दद्यादास्तन्यपर्याप्तेर्बालानां वीक्ष्य मात्रया। ( सु. शा. १०/ ५३)

Milk is the only congenial diet to child, when mother or wet nurse are unable to feed the baby, goat or cow milk should be given in appropriate amount.(the quantity by which the baby feels satisfied.)

Astanga sangraha:

स्तन्यभावे पयश्छागं गव्यं वा तद्गुणं पिबेद्।

मूलैः सिद्धंबृहत्याद्यैस्थिराभ्यावासितायुतम्। (अ. सं. उ. स्था.१/ ३९)

when the mother's milk or wet nurse milk are not available to feed the child, goat or cow milk can be given in appropriate quantity.

This milk should be processed with बृहति, कण्टकारि, शालिपर्णि, पृश्निपर्णि, गोक्षुर and mixed with sita(candy sugar) and given to the child in appropriate quantity.