I completely understand how you feel, I have been there. But I would strongly recommend you stay clear of anyone who is offering a free tummy tuck as a trainee. Do you really want to be practised on? An abdominoplasty is massive surgery and one where the surgeon requires great skill and experience. Think about your children, is it really worth taking the risk? You could end up in a much worse position than you feel you are in now. There are risks of infection, thrombosis and can you imagine if it went wrong you would still have to live with a stomach you are not happy with.
I know this is probably not what you wanted to hear, but I hope it rings some alarm bells for you.