I’m going to take a guess here.
1. He’s two that’s the first factor.
2. No food in the house or parents not feed him for hours so booze goes in on empty stomach.
3. He’s also thirsty, so consumes it quickly and with 1 and 2 in place the booze crashes his system.
All that you suggest is certainly possible, but my guess (and it’s just that—a guess—at this point) is that his mother and her boyfriend thought this was funny and gave him more than one drink. Then they lied about how much they gave him.