Considering nursing the runt, Need suggestions/advice!

I got a better look at the kittens today, as I was able to get some video and review it and It makes me a bit concerned for the runt. He seems small BUT he does eat. While I was feeding mama he was eating alright. Ive seen him fight for nipples before but I believe since there are four of them he always manages to find one...he just likes to go after the ones of his littermates is always on.

If I understand this right there is always a runt in a litter? Its simply a smaller kitten that started its gestation a little bit later then the others? Im considering giving him some KMR just to help boost his nutrients although Im sure he does get mommas milk. I just want advice on how about going about taking him from momma to nurse. Should I just try to take him out while shes in the box?

This weekend we are testing waters with the new mom...going to try petting the kittens. She let my sister pet them a little bit earlier, but we have since then moved the nest and dont want to make her to stressed with us interfering to much, to close together.

I really would just like some advice on how more experienced folks handle supplemental nursing for the newborns. 

Thanks!

Are you weighing him each day at about the same time?  If not it's the best way to keep track of his progress and see if he actually needs supplementing.  Ideally weigh in grams, and he should put at least 10g on most days.  If you want to weigh in ounces you need to have a scale that will weigh to 1/10 oz, and find out what 10g is in ounces - it's a nice round number that's easy to remember.

*if* he isn't gaining then yes, supplement, but remember 1) feed him in the position he suckles in otherwise milk can go down the wrong way which is usually fatal, 2) cleanliness is essential, 3) so is making up the feed accurately.

BTW all litters must have a smallest kitten, but unless he's a LOT smaller and/or struggling I wouldn't call him a runt.  I've never considered I've had one in any of the litters I've fostered, or any of those my friend's cats have had.  The smallest kitten in a subsequent litter the mother of my my first two cats had would go round all the teats when the two larger kittens weren't feeding and did just fine.