Bro question! Question from a bro!
Do you have a problem with the quantity or the quality? If the sex is still hot, then twice a week sounds pretty... normal. I mean, you both have kids. I assume you're both working. If you're like most adults, your life is busy. Hectic schedules. Long days at the office that end with one desire: pizza and CSI. Finding a couple of times a week to bang it out sounds about right six months into a relationship between two complicated people with baggage (joyful baggage? Is that a nice way to say "kids"?)
But you have needs and I'm not dismissing them. I'm guessing rubbing a few dozen out a week doesn't do it for you, heh? A healthy relationship is one where two people can sit down, reveal what they need, and negotiate how to get that. I'm going to go ahead and guess that the problem is finding the time. Because if she's giving it to you twice a week after six months, then I'm guessing she's still into you. So when you talk to her about how you want more sex, don't couch it as a problem that she's not giving you enough, and you're a sex glutton who wants more, more, more. Talk about how the two of you can find more time to be together. Time away from work, stress, kids. Look at your schedules and try to carve out an hour here, or a whole afternoon there. And then make that time special. It's like zen, man. Catch what you want by not chasing it. Get sex by not trying to get sex.
Talk to your woman about making more time where it's just you and her. Where you can both just spend time with one another and be. Make each other laugh. Have a glass of wine. Play a board game. Naked.
And the sexy wisdom of JDV strikes again! You're amazing, and completely right. I'm guessing she'd probably like more than twice a week, too. So, tell her. Let her know that the 2x are fabulous and just make you want her more, more often. Explain that logically you know you're both giving everything you have, whenever you have it. But, you miss her in between. If sex is the touchstone of your relationship (i.e., you talk, you get together en famille, etc.; but sex is your one-on-one, just us time), tell her that you're not touching your touchstone enough. You know "you miss her". Like that. I think it ain't about getting off (see JDV comment re: rubbing one out), but getting together.
Having sex with someone else other than the father/mother of your children (assuming he/she is still alive) is really weird!