There are times when I am completely exhausted from work and from taking care of my children. In the evening I would very much like to go to sleep. I feel that I would function much better the next day if I could go to bed early and get a good nights sleep (children permitting). However, especially in the summer, I feel that I need to stay awake in order to daven Tefillat Maariv at the right time and with a Minyan. Am I obligated to stay awake to daven - or if a person goes to sleep before the time of Maariv is this acceptable?

The Talmud teaches (according to the opinion that is adopted l'halacha) that Tefilat Arvit reshut - Ma'ariv is optional, Tosephot interprets this to mean that arvit is obligitory unless there is another Mitzvah to do, in which case Ma'ariv is optional compared to the other Mitzvah which may take precedence. According to the Rambam, Ma'ariv was originally optional, but we have accepted it as an obligation so that today it is obligatory. Therefor, it would be difficult to exempt you from Ma'ariv entirely (though according to Tosephot it could be considered). Following are the suggestions I would make. You may forgo Ma'ariv with a Minyan. You may take a nap before dovening if you set an alarm. If you are worried you won't get up, you may doven Ma'ariv before sunset (after Plag Hamincha), the same way some doven early on Erev Shabbat, as long as you re sure that you will say Kri'at Shma after nightfall. All of these solutions are possible in situations of duress (I count your situation as such) but are not general rules.