Very sorry to hear about your loss. May he be in peace and be blessed.
In your own chart, your progressed Moon had just entered your 9th house. Normally, when the progressed Moon enters or leaves a house, there is usually activity. I would have thought, just by looking at the fact that the Moon had entered the 9th, that either you have started some uni course, something impactful with the overseas has happened, or spiritual awakening. When we go a step further, the Moon was square natal Pluto (impactful transformation).
Though we have to look at the 5th house foremost for children, in general, but the 7th is also considered due to his being your 2nd child. Lord of your 7th house is Mer, and your prog Mer was on the natal 5th house, closely squaring Mars (ruler of your natal 5th house). That same prog Mer was in a little over 1° sextile to Jup in the 7th also, so, again showing the 2nd child (but through compensation, sorry). The aforementioned is also endorsed by Jup itself transiting the 5th and also sextiling natal Jup in the 7th. This also means that prog Mer and transit Jup were conj one another. May I ask, if it happened in the morning/forenoon. Transit Mars was retrograde, in Virgo, so also ruled by Mer (ruler of your 2nd son) and was in direct opposition to natal Sun (Sun rules the male child in the mother's chart). Saturn had separated from a square with Moon (mothering) and applying in a trine to Jup in natal 7th house, so you see how the 7th house was though attacked (through its Lord; Mer mostly), but was also blessed through many wonderful aspects to Jup (fortune) there. Transit Ura (change) over the 4th house (family), was squaring Jup in the 7th tightly as well. One doesn't normally conclude a sad mishap as this, but otherwise one would have though instability in relationship. Finally, if you will notice the degree on transit Pluto it was exactly the same as the cusp of your 2nd house (existence was shaken), and this in conj to Ura.
The natal Moon is afflicted by Sat. If the natal Moon is either in the 5th or 11th (5th-11th axis denotes children) house, and afflicted by Sat or Mars, it may denote such a mishap. Or else, through its affliction by Sat a difficult childhood for the child, sometimes even phyiscal deformities. Through affliction by Mars, it may denote a child that is a difficult caesarian (Mars) birth, or with some problem with the blood (like extreme cases where blood transfusion is needed). At least, Sat-Moon in the mother's chart will show a later or a difficult pregnancy. Fortunately, in your chart, the Lord, Mars is in conj with Ven (fortune) and not afflicted otherwise either. You also have the Lot of fortune in the 5th. Please feel free not to answer if you don't like to, but may I ask if you are pregnant with a male child?