Some maintain that all those dying in infancy are regenerated. Spurgeon attempted to demonstrate this from 2 Sam 12:23 (New Park Street Pulpit, 1861, p509).

If infants are saved, it must be on the basis of redemptive grace, Jn 3:3; 1 Tim 2:5. Scripture indicates that it is possible to be filled by the Holy Spirit from an early age, Lk 1:15, cf Ps 22:10. This implies an intuitive knowledge of God, apart from usual process of hearing and understanding the gospel. Moreover, there does appear to be a pattern in Scripture whereby God blesses the children of those who believe in him, Gen 7:1; Heb 11:7; Jos 2:18; Ps 103:17; Jn 4:53; Acts 2:39; 16:31; 18:8; 1 Cor 1:16; 7:14; Tit 1:6. There are, of course, exceptions to this, such as Esau and Absalom. See esp. 2 Sam 12:23. (See Grudem, Systematic Theology, 499-501)

‘If one argues for the salvation of all children dying in infancy one must do so, it seems to me, on general theological grounds – the goodness of the nature of God, the known character of Jesus Christ, the ways of grace, and the multitudinous number of the saved which must, according to Spurgeon, include a majority of infant souls. My difficulty with this approach is that it is inferential, and that it is not supported by any plain and unequivocal declaration of Scripture. I prefer, therefore, to say that, while I hope that all infants dying in infancy may be saved, I do not know that they are, because God has not seen fit to say so in his Word. Nor do I accept that this is to take a pessimistic position. Rather would I argue that it is the only prudent one to take. Where God has not seen fit to reveal, we must keep in silence.’ (David Kingdon, Q in A Faith to Confess, 13)