Alec is a robot built by Shanna.
This explains his behavior in some of the issues, such as Fit to Win, in which he clearly is not a normal child. When he mouths off to Superman, she realizes that his programming is malfunctioning.Alec and Shanna are stepsiblings.
There are two issues, and one in particular, which suggest that they live in the same house, even though another issue clearly has them communicating with their computers to play chess over the internet. My theory is that sometime between issues, they played matchmaker for their single parents. This would also explain why neither parent looks like either of the kids; it could be extrapolated that they each resemble their biological parent who isn't there.Alec and Shanna are responsible for the destruction of Coast City.
The Fit to Win comic shows that Alec and Shanna are students at "Coastal City Elementary" according to their booth banner, but the name does not appear anywhere else in the DC universe comics, media or wiki. This implies that this is most likely a nickname for Coast City. Considering that the Tandy Computer Whiz Kids stopped publishing shortly before the destruction of Coast City, it's highly likely that their constant meddling with Tandy computers eventually attracted the attention of Cyborg Superman who reported to Mongul of this location, leading to its ultimate destruction at their hands. Lack of further appearance in any DC comics of Alec and Shanna leads to the conclusion that they died as the result of this event which they unwittingly triggered.