Putting the terminology aside for a minute. That's not necessarily the point. Are children saved by virtue of being children or are they separated from god after death for eternity?
God is the judge of a person's heart.....no righteous person will lose their lives by God's hand. But God has his criteria for salvation and what he considers as "righteousness". We can't tell the judge to carry out justice......his justice is perfect, based on his stated laws, not on sentimentality. This is a God who knows the heart, not just the actions. It matter more to him what our motivation is, not the performance we carry out.
The usage of universal salvation, heaven, and hell et cetera are used to make this point. Obeying rules and the obligations a christian has to god and scripture as an adult isn't related to the question.
Since Jesus himself used the flood of Noah's day to illustrate the situation that we would face again, (Matthew 24:37-39) how many children survived the flood? Why do you think only Noah and his family survived, when everyone outside the ark, perished? Were the people prevented from coming onto the ark? Did God prohibit any of them from saving themselves? Noah was called a "preacher of righteousness" in an unrighteous world....(2 Peter 2:5) so they knew what the message was...but they just chose to ignore it in much the same way as people do today.
He said
"they took no notice until the flood came and swept them all away".....and we believe that it will be that way again with the nay-sayers and unbelievers.
Ignoring Noah's warning and treating him with disrespect is what claimed the lives of those people, as well as their children.
So we need to put the blame where it lies. The invitation was open to all, and for a very long time, but nobody took it up, choosing instead to stay with the violence and immorality to which they had become accustomed.
Violence and immorality can become accepted when people are exposed to it for a long time.....much of today's violence and immorality is served virtually, via the entertainment media. Children are raised with very violent video games and movies where no imagination is needed as the carnage and immoral conduct is portrayed very graphically and accepted as "normal"....just harmless entertainment. Don't we have to ask why humans have such an insatiable appetite for those things?
If we have a sense of morality like no other creatures, is that appetite, normal or abnormal? The Bible calls that appetite..."sin" and it is in all of us. But its up to us whether we treat it as "normal" or not.
The apostle Paul also explained an interesting fact regarding a child's standing with God....
"....If any brother has an unbelieving wife and she is agreeable to staying with him, let him not leave her; 13 and if a woman has an unbelieving husband and he is agreeable to staying with her, let her not leave her husband. 14 For the unbelieving husband is sanctified in relation to his wife, and the unbelieving wife is sanctified in relation to the brother; otherwise, your children would be unclean, but now they are holy." (1 Corinthians 7:12-14)
If a Christian has an unbelieving mate, God views them as "sanctified" because of their children. This means that there is an age of accountability where children are concerned.....but it is not numerical, it is an age where a child can choose to worship God on their own. Spiritual maturity knows no age. So, before that time they are on their parent's 'ticket' (so to speak) and will be saved (or not saved) by virtue of their believing parents' standing with God.
Does that answer your question?