M.,
I also can totally relate and I second all the recommendations for magnesium before bed (either the Calm recommended by Alene or in a capsule - magnesium glycinate is easy to digest and absorb. Be careful not to take more than 300 mg at first as it can give you diarrhea. Magnesium is responsible for helping muscles to relax, including the bowels!).
For me, I always felt "on duty" when I went to bed. My brain was listening for the tiniest indication my son needed me and I often dreamed he was calling out for me, waking me as a result! So my husband agreed to be the point person for night time awakenings. This really helped me mentally. Your children might not be old enough yet for this (until my son was about 4, it was always mama or no one to help at night). I close the door to the bedroom (hubby doesn't usually come to bed until much later) and I am able to sleep better knowing he can handle most anything that comes up.
Another recommendation would be to take L-tryptophan, which is an amino acid your body needs to produce serotonin. Serotonin in turn becomes melatonin, which is the hormone that regulates sleep. I take it during the winter as I find I am affected by seasonal affective disorder and in particular my sleep worsens as a result. L-tryptophan is a little hard to find. Natural health food stores should carry it (you can also buy online). I take 1500 mg in mid afternoon and another 1500 right before bed (but start out with 500 mg and work your way up to this over several days). This is not something you want to take long-term, but rather, just to re-train your body's systems and replenish your serotonin levels. You should take it with 50 - 100 mg of B6, which your body also needs to produce serotonin.
Also, I would try to eliminate all caffeine for a while, or limit yourself to no more than 3 cups of green tea per day (this is about 45 mg caffeine). When your adrenals are pumping out stress hormones, as it sounds yours are, the extra caffeine actually stimulates more cortisol production. Sugar and refined flour have the same affect, as does alcohol. I would recommend either chamomile or Tulsi teas before bed. Tulsi teas are made with Holy Basil, which is an "adaptogenic" herb -- it literally helps your body maintain balance and reduces cortisol levels.
Finally, I would find some meditation CD's to download on your iPod and listen to them in bed each night. I found that after doing this consistently for 2 to 3 weeks, I was able to fall asleep and stay asleep much easier.
Best of luck to you. I think most young mom's have similar concerns and we just need to remember that we have to take care of ourselves 1st because if we aren't functioning well, the family doesn't function well. Whatever time or money you need to spend to reduce your stress and be able to sleep well is time and money well spent!
A.