Can a mom get custody back from her parents who adopted them?

I lost my children to dhs 8 years ago, I signed consent for my parents to adopt my 4 beautiful children after going 2 years without seeing them. At that time I was unemployed, homeless and just letting go a drug habit. We all just wanted dhs out of the pic and now i have had them living with me more then 70% of the time during school for lil ovr 5 yrs. i wld pick them up from parents home after school everyday or they wld get dropped off by one of parents, i dropped off every morn for school. all this way was fine til this past dec 2010 when husband and i asked for them to feed kids before sending them home from school cuz we were finan strapped. feb 10, 2011 they came and took them back. i now get them on friday evenings and drop off monday morns til school got out. then feels like i am expected to take them all back on full time..... i just want custody of my babies. i have been sober for 6 years, own my home (well pay mortgage n e way) full time machine operator i am and also a full time student for associates in computer programming. what in the world should i do? oh and bout 8 yrs ago i got a felony convic of knowingly concelling stolen property when ex husband was out robbing people. good ridance to him.....