Serger: constantly rethreading the bottom looper!?

I am very very new to serging, I have a used Kenmore and everything was going great. Then my 2 year old daughter got her hands on it while I was at work, pulled off the tension knobs and broke some of the thread. I rethreaded the whole machine, I've replaced the knobs and tinkered with the tension so the stitches come out beautiful again. My problem is that I sew a seam, stop, cut the thread, then when I go to sew the second seam, the last part of the bottom looper is unthreaded again!! Help me please!!!!!!!!!!