Should I stay or should I go?

My supervisor told me today that the 'big boss' is likely going to be pushing me soon to accept a full-time posotion. I currently work 20 hours a week, and it works very well for me and my family. Plus, I don't really love my job. There are some parts I can't stand (one doctor in particular who shall remain nameless...) but I do love my clients. Most social workers can't claim that. Overall, it's a good job.

They are not forcing me yet, but I am afraid that might happen soon. It has been this way for basically the two years I have worked this schedule, and my job has never been stable (it's non-profit, grant-funded) in the 5 1/2 years I've been there.

I am not sure what to do. We could surely use the money, but I am not sure that the money is worth losing the experience I am getting with my son. Plus, we are considering having another child soon, and if that happens, I will NOT work full-time. I do not want to be in the position to have to re-negotioate my job all over again.

I would go somewhere else, but my schedule is pretty consitricted due to having to work around my husband's. And if I go full-time, it means we'll need to find a day care provider I trust - and I don't even really trust our parents, who are the only ones who have ever watched our child.

I had some extremely bad experiences in day care when I was a child and I will not let that happen to my son. I know there are trustworthy people out there, but will I ever be able to trust anyone?

And can they legally force me to choose, when I have a contract stating my position is part-time? I even agreed when I signed it that should I want to return full-time, that they would not be obligated to give it to me.

I am so torn.

My options:
-Return to full-time, in order to keep my job, and put my child in day care. My husband wouldn't necessarily be able to change his schedule, so this would also mean NEVER seeing him.
-Stay as long as possible with my current schedule and risk losing it one day because they decide they can't continue to keep me at part-time. (Plus, this way I face excessive scrutiny because they are looking for any reason to fire me. Right now, since they can do nothing based on my stellar job performance, they are picking apart my unplanned absences. I was out twice, for two days a piece because I was sick. Really sick. And I work with immuno-comprimised people who can't afford to get sick. They are counting that as four days against me, not as two seperate instances, even though every other day I have taken off - four days - have been scheduled. Plus, this is all accrued PTO, so it's time I have to take.)
-Get the hell out of there and find full-time employment elsewhere (I've looked, there are no part-time jobs in this area, in my field) - where most likely I'll deal with a whole other load of crap... Plus have to leave clients I love and co-workers who are awesome (Jenn!)

I feel so stuck! Help!?!