Your question assumes that people go to heaven at death. The Bible does not teach this — this doctrine has been developed by men partly as a result of misunderstanding some passages of Scripture. Consider the following Scriptures:
Eccl 9:5 For the living know that they will die, but the dead know nothing…
Psa 115:16-17 The heavens are the LORD’s heavens, but the earth he has given to the children of man. (17) The dead do not praise the LORD, nor do any who go down into silence.
Psa 104:29 When you hide your face, they are dismayed; when you take away their breath, they die and return to their dust.
The above verses show that the dead are unconscious and know nothing, a situation which could not be, if people went to heaven at death. The following verses indicate very clearly that people do not go to heaven when they die:
John 3:13 No one has ascended into heaven…
Acts 2:34 For David did not ascend into the heavens…
John 3 states that no one has gone to heaven and Acts 2 states that David, the man after God’s heart (Acts 13:22), did not go to heaven.
The hope that the Bible speaks of, is resurrection and immortality given when Jesus returns to earth. See the following verses:
Dan 12:2 And many of those who sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt.
Isa 26:19 Your dead shall live; their bodies shall rise. You who dwell in the dust, awake and sing for joy! For your dew is a dew of light, and the earth will give birth to the dead.
Isaiah 26 is a very poetical prophecy of the resurrection, speaking of the wonderful time when at his return, Jesus raises the faithful who are sleeping in the dust of the earth, waiting to be awakened from the sleep of death. Repeatedly we read when the dead will be rewarded – at the last day – the day when Jesus returns to earth.
John 6:44 No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day.
1Thes 4:16 For the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God. And the dead in Christ will rise first.
1Co 15:51-54 Behold! I tell you a mystery. We shall not all sleep, but we shall all be changed, (52) in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised imperishable, and we shall be changed. (53) For this perishable body must put on the imperishable, and this mortal body must put on immortality. (54) When the perishable puts on the imperishable, and the mortal puts on immortality, then shall come to pass the saying that is written: “Death is swallowed up in victory.”
So our hope is in the resurrection at the return of Jesus. The question is, will all children be saved? The Bible does not say this will happen. However, it gives several indications (in my opinion) that the children of believers will be resurrected. For example:
Isa 65:23 They shall not labor in vain or bear children for calamity, for they shall be the offspring of the blessed of the LORD, and their descendants with them.
Isaiah 65 is speaking of the time when Jesus is king over the earth. Reference is made to the mortal descendants of the blessed of the Lord, which I take to be the children the saints had in this current dispensation. We know that the immortalized saints will not have children, as Jesus tells us that they will not marry in Luke 20:35, so Isaiah 65:23 must be a reference to the children of the saints who have grown up and are bearing children in the Kingdom age.
We also know from 1 Corinthians 7:14, that the children of believers are special in God’s sight. Another passage that gives a hint of the resurrection of children, is in the prophecy of the children slain by Herod, when the wise men sought to pay homage to the child Jesus:
Jer 31:15-17 Thus says the LORD: “A voice is heard in Ramah, lamentation and bitter weeping. Rachel is weeping for her children; she refuses to be comforted for her children, because they are no more.” (16) Thus says the LORD: “Keep your voice from weeping, and your eyes from tears, for there is a reward for your work, declares the LORD, and they shall come back from the land of the enemy. (17) There is hope for your future, declares the LORD, and your children shall come back to their own country.
I believe that the assurances from God to the distraught mothers, indicate that at the resurrection they will see their children again.