I know how are it can be getting into the exercise groove especiall with kids...I always say some exercise is better than no exerise. Here are some ideas you can use if you have small and large children.
Walking - walking is good for all ages and encourage your children to ride their bikes while you walk or push your baby in his/her stroller while you walk
Jump rope - hula hoop with your kids..this is fun and easy and gives you time with your kids. Did you know that hula hooping is great for your waist line...incorporate weight lifting...If you have a young son he will love it!! Buy him a very light weight (a pound or less) watch him go.
Dancing is a great way to exercise, buy exercise videos that require dancing or just turn up the music and watch your kids go..so what if you are not a good dancer just keep it moving. Let your kids teach you the latest dances..how fun.