Babylon 5 - can anyone explain to me who is Sheridan's child and what is going on (what about that 'parasite' that Sheridan was supposed to give his child when he was 16)?

I can answer this! The 'parasite' was called a Keeper. If you watched the second last episode, watch the scene where Londo gives the 'vase' to Sheridan and Delenn. There's a moment where Delenn sees something on/near Londo - she's sensing the Keeper.

The Regent had a Keeper and when Londo became Emporer, he was given one as well. The Keeper 'keeps' whoever it is attached to and makes sure it does that the Drakh (evil race) want it to. Londo gave the keeper to Sheridan and Delenn so that when their son turns 16, the Centauri/Drakh will be able to control their son and eventually lure him to Centauri Prime - knowing that Sheridan and Delenn will love their son and come after him.

So, if you've ever seen the episodes 'War Without End,' that's what Sheridan and Delenn are doing on Centauri Prime in when Sheridan travels to the future - they are trying to save their son.

If you want more information, a GREAT place to go is the Babylon 5 forum at: http://www.b5tv.com [bboard.scifi.com/bboard no longer exists] it's on the SciFi channel website. There are people on there that know every little detail and they're a nice bunch of people (including the couple of people who are a little...odd!)