Getting started in Aid work

Hello,
I am a woman in my late 20's, I am a mechanical engineer by profession btu I have taken a couple of separate months out from work do to volunteer work, once in Costa Rica, teaching music in a local scheme giving lessons to children from all over the area who can't afford this kind of education. Secondly in Tanzania working in an orphanage, caring for and tutoring the children.
These experiences gave me a new outlook and I have come to wanting to do this kind of work full time. Short term volunteerign can be expensive and requires a willing employer who doesn'tmind you popping off for a bit.

I am wondering how to get into this in a more permanent way. I dont' have any qualifications for aid work or with children or anything like that, are there posts in the field that you don't need qualifications or can anyone advise me on some training that may be useful.

Basically I would like any advice I could get on getting started in this field, good orgaisations to look at etc. It's a big change to make from a stabel 9-5 job so I want to gt my facts straight before making any desicions, I think this is especially important for a woman travelling alone.

Thanks very much