I'm thinking of possibly getting a DNA test done on my kids without my wife knowing.
In secret? Why would you keep a DNA test secret from your wife?
Two reasons. One, their noses looks different from mine and also my wife once gave another guy a hand-job while he was driving.
It is understandable to have doubts if your kids are yours or not when they do not look like you, but you should not get them DNA tested without your wife knowing it. You should not do things concerning your kids behind your wife's back. You need to speak to her about the testing.
Why should I? She snuck around first. I just want to find out if I'm their biological dad.
Keeping secrets from your wife isn't the way to have a healthy relationship. It will just make you resent her if you don't get the answers you want, and it will make her resent you if she finds out you were going behind her back. You should communicate your worries to her openly and sensitively so you can resolve it together as a husband-and-wife team.