Trying to lose weight

I am almost 27 years old and I have struggled with my weight my whole life. I guess you can say I was slightly overweight in high school but it didn't start becoming a problem until I was pregnant with my daughter. I gained so much weight during that pregnancy and have struggled with it since. I had another pregnancy where I didn't gain any weight but I didn't lose any either. I am at my heaviest weight right now at about 280 and it kills me to look in the mirror and see myself. I have tried many different times to exercise and lose weight but I get truck in a rut and when I don't see any change I just slowly stop doing it. I don't know how to keep going. I don't know where to start and how to keep it going. I want to be healthy for my family, I want to be able to play with my kids and not get tires 5 mins after playing and have to sit down. My kids are 7 and almost 3, this is prime time for me to be active with my kids but I just can't keep up...