Ya ha! I've noticed that at least one parent has similiar connections to that of at least one of the offpsring (haha sounds like we're on the discovery channel here) and even if the sun signs aren't the same, placements in houses or moon signs often indicate similiar energies.
Eg. Aquarius dad, Taurus moon Cancer mum, Libra moon
Aquarius = me, sun in fourth (house of cancer), Taurus sister with Libra moon
Very basic example but I see it pop up very very often, and if not, the children have other similarities that they're not even aware of with different aspects of the chart. So its not just in the genes eh??

Here's an interesting web link I came across...

www.janetboyer.com/Articles.html