Well, how do i get the stat points back, that vampire (who was about to kill the child) stole me? i told him to choose me instead of the child and now im weakened. how do i get my strength back?

I've always taken it that the stat losses are the price you pay for saving the child. I regain them through the normal channel of increasing strength etc., when the points are available as you go up a level or two. So you re-coup them via normal character development as related to playing the game.

That is a permanent loss of 1-4 stat points (most commonly 3). However, there are several bonuses in the game that give you stat points and even entire levels (ie enough experience to get to whatever the next level is).

and do you benefit from saving that child? Do you get a small compensation? otherwise ill just let him kill the child and then kill the vampire. I'm a pefectionist when it comes to gaming. i couldn't live with the fact, that i have permanenty lost 3 stat points. thats why im stuck at the thieves guild part, where you need pickpocketing. i want to play but i'm hesitating to "waste" points on that skill...

Just that quest (and if you talked to the knight west of there beforehand).

In Verdistis the guy in the cellar has a quest for you to steal an item that gives you a +20 Agility bonus (so it is best to not complete the quest). There is a shrine somewhere around the dwarven village that will give you a random +5 or -5 bonus to a stat. Not to mention charms and equipment bonuses...

You can find Pickpocket bonuses on jewelry, so if you keep an eye out when checking merchants (or reload at Kistandalius in Ars Magicana or Corinna in Verdistis) you may not need to 'waste' a skill point to join the thieves guild.

When I met the knight to the north, he gave me an ability as a reward for having done the right thing. Don't know if he would give it otherwise. Bless is not the skill I use most, sure, but it kinda sweetened the pill. :)

(And 3 point is not much in this game, frankly. At least not for me when the tradoff is to play my character "right". Many items can and will give you far greater bonuses)

Since that kid doesn't have any other meaning than being part of a "hero or a**hole" encounter, i'm going to let him kill the child.