How can there be love in heaven when sinners are in hell?

Answer:

Your son appears to have concluded that love and justice are incompatible.

"Beloved, let us love one another, for love is from God; and everyone who loves is born of God and knows God. The one who does not love does not know God, for God is love. By this the love of God was manifested in us, that God has sent His only begotten Son into the world so that we might live through Him. In this is love, not that we loved God, but that He loved us and sent His Son to be the propitiation for our sins. Beloved, if God so loved us, we also ought to love one another" (I John 4:7-11).

We must note that this passage and many others like it are addressed to Christians. God's love is manifested for all the world in that He sent His Son to the world to die for us so that we might live with God. God did not have to do this. He could have justly written each of us off when we sin because "the wages of sin is death" (Romans 6:23). But God went out of His way to offer us salvation.

"For while we were still helpless, at the right time Christ died for the ungodly. For one will hardly die for a righteous man; though perhaps for the good man someone would dare even to die. But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us. Much more then, having now been justified by His blood, we shall be saved from the wrath of God through Him. For if while we were enemies we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life" (Romans 5:6-10).

Notice that God's wrath still exists. Wrath against whom? Against those who still refuse God's offer of salvation. We are not saved while remaining in sin. We are saved from sin. "What shall we say then? Are we to continue in sin so that grace may increase? May it never be! How shall we who died to sin still live in it?" (Romans 6:1-2). Love for God is shown in our obedience. "Whoever believes that Jesus is the Christ is born of God, and whoever loves the Father loves the child born of Him. By this we know that we love the children of God, when we love God and observe His commandments. For this is the love of God, that we keep His commandments; and His commandments are not burdensome" (I John 5:1-3). God showed love to a lost and dying world. God loves His children. But God does not love those who refuse to accept His generous offer and continue in sin. "The LORD tests the righteous and the wicked, and the one who loves violence His soul hates. Upon the wicked He will rain snares; fire and brimstone and burning wind will be the portion of their cup. For the LORD is righteous, He loves righteousness; the upright will behold His face" (Psalms 11:5-7). God's love doesn't cancel God's justice.

Those who will be condemned to hell will be there because they refused the multiple opportunities from the loving God to leave their sins and become His child. It isn't what God or any Christian wants, but it is what must be because it is what each sinner has chosen. "For we must all appear before the judgment seat of Christ, so that each one may be recompensed for his deeds in the body, according to what he has done, whether good or bad. Therefore, knowing the fear of the Lord, we persuade men" (II Corinthians 5:10-11).