In Jeremiah 19:4 God refers to the children that have been sacrified to Baal (v. 5) as innocent. The word innocent would mean not guilty and therefore found as innocent before God.
In the New Testament, In Mark 10:14, Jesus reminds us that the Kingdom of God belongs to such as children. He proceeds to bless them (v. 16). This is the same word he uses on those who mourn, who are humble, etc in the Beautitudes, to refer to their rewards. When he saw that the people were holding the children from him, he used a Greek word, ηγανακτησεν which means strong displeasure, indicative of his strong disapproval of withholding such children from him.
Believers are saved through faith alone (Mark 16:16; John 3:15; Rom. 10:9; Eph. 2:8). Whilst previous Scriptures appear supportive of children and infants who die going to heaven, these people still need to be saved through faith as we learn from, inter alia, above mentioned Scriptures that faith alone saves.
To sum up:
1. Faith alone saves all sinners per Romans 3:23-24. As God chose us in him before the foundation of the world (Eph 1:4), if infants are of the elect they would have been chosen before they were conceived and God would through him enable those people to have faith.
2. The Almighty is just and cannot do wicked (Job. 32:12).
3. We are certainly in no position to guide or counsel God (Is. 40:13).
4. Our minds can surely not understand that of God’s (1 Cor. 2:16).
5. Finally as we serve a God who is loving per 1 John 4:8 (but primarily just and holy), we are also guided not to be anxious but to put all requests in prayer and supplication to God to receive peace which will guard our hearts per Philippians 4:6-7. Jesus also guides us that although we are wicked, we can serve our children, so how much more will our holy, just and loving Almighty Father do per Matthew 7:11.