Megan Fox tries to work less than 20 days a year.

The 'Teenage Mutant Ninja Turtles' actress - who has two young sons, Noah, 20-months, and Bodhi, four-months, with husband Brian Austin Green - admits she constantly feels guilty about not spending enough time with her family, but claims she can't afford not to do one movie a year.

The 28-year-old star told Parents magazine: ''I have to make one movie a year because I have to invest in their future and I have to be able to pay their way through college and be able to provide for them. I'm looking for movies that will shoot in Los Angeles, for projects where I'm part of an ensemble so I can shoot in and out in 10-20 days. It's all about trying to spend as little time away from my kids as possible.''

Despite her chosen profession, Megan refuses to let her sons watch TV and sometimes struggles to find ways to keep Noah entertained.

She said: ''Before you have kids, you really do not understand how much work it is and how consuming it is.

''It's really hard to manage because I also don't let them watch TV. It's not like I'm going to sit Noah in front of the television so I can take care of Bodhi. I have to figure out how to incorporate Noah into the process and have him help me take care of Bodhi and make sure he doesn't get jealous and make sure nobody's neglected and everybody's needs are being met. As a mom it's hard because I don't feel like I'm ever giving either one of them 100 percent of my attention or 100 percent of myself, so I carry a lot of guilt.''

The brunette beauty finds it hard to relax because she is very protective of her children.

She said: ''I had no idea how worried I was going to be for the rest of my life. From the moment I gave birth to Noah, that was the first time I was like, 'I love something so much that I will never be the same again.' ''