Reference: Fataawa ash-Shaykh al-‘Allaamah Muhammad Naasiruddeen al-Albaanee fil-Madeenah wal-Imaaraat – Page 123;
Fataawa al-Madeenah – Page 18
Question: Are infants performing hajj required to slaughter the sacrifice?
Response: Whoever wants to make their infant child to perform hajj, then he is required to implement [all] the rulings [related to] hajj, just as he implements them upon himself; And from them is [to slaughter] the sacrifice.
So if he was unable to find a sacrificial animal, then a ruling related to it has been prescribed – and that is he must fast on his [infant child’s] behalf.
And this is what is apparent to us from what we haveunderstood, as well as what we have derived [from the Qur.aan and the authentic Sunnah]. And Allaah [alone] has the Complete knowledge [of all affairs].