The entire Eastern Orthodox communion teaches that people do not inheret original sin simply by being born. However, children do inherit the consequences of orginal sin by being born into a world currupted by people who have repeated the sin time and time again. In a sense, original sin is something we are socialized into. I like much of what Augustine wrote, but it isn’t necessary to believe everything he ever wrote.
Also, heaven and hell are not static states. Limbo simply denotes the infants, not having had an opportunity to develop sanctity, can only comprehend the love of God in a way proportional to their ability. Again, the Orthodox make the most sense when they say that heaven and hell are the same reality precieved in different ways. We need to pray that God will love this unborn child. We know God loves all his creation and, therefore, we can rest our mind at ease.