I am trying to find the inn where I am supposed to meet the assassin who can cure the poison I was infected with. When I get to where it says the Blade and Stars inn is on the map of Baldurs Gate and enter all I find is a kid who says that he travells with his father. Is the map wrong? or is there something that I am missing.

The Blade & Stars is a huge building accessed from the west side of the map where the Elfsong Tavern is. Once you move maps just keep walking west along the main street, you can't miss it.

PS Forgive my ignorance as it's been a while since I played BG1 but isn't the assassin at the Blushing Mermaid?

Hells Bells, I can't find that inn either and it seems like I am too dumb or something to follow these directions... is the Blade and Stars in west of Elfsong???

The Blushing Mermaid is one of the most difficult places to get to, because of the bloody second wall. It's in the district sliced in half by said wall... look on the map. To get to the Mermaid, I believe you need to travel to its district from the northeast corner of the district with the Elfsong tavern... If it's not that, just keep trying, always from the southeast.

Lothander (the 1st assassin) is on the 2nd floor of the Blade and Stars Inn. To get there, walk to the door of the Elfsong or just to the entrance of the Sorcerous Sundries (either 1 will do). (If you don't recognize either of these buildings, then it maybe it will help if you know that this is also the area where the Thieve's Guild is). From there move southwest from the sorcerous sundries or move south or west from the Elfsong till you move to the edge of the map. If you click onto your map screen, the circle(s) identifying your player(s) should be on the far west edge of the screen. Go west by just one area and you'll be on a different map. This time, move to the far Northwestern corner of this area. The Blade and Stars Inn is there ;) .

Memnoch, the second assassin (Marek) is at the Blusing Mermaid. He's the one that actualy cures you of the poison, although you don't need to drink the antidote that he drops to be cured.

The way I get into the Blusing Mermaid is by going to the area where the Duchal Palace is and I walk towards Ramazith's Tower (you can't miss it, it's tall and huge). Then I just move a little east from there till I'm on the edge of the map and move eastwards to the NE part of BG, where the Blushing Mermaid is.