What is the best excercise to tighten abs after having children?

Weight loss, strengt: Get to ideal body weight which is 100 lbs for first 5 feet tall and then allow 5 more lbs for each inch taller than that for females. Daily routine is: lie on carpet or pad, place a 3 inch padded tube under your lower back, keep feet raised off of floor, then do 50 sit ups (meaning touch shoulder blades on floor and then flex spine as much as possible, then repeat. That is, move spine, not hips).

Refer to answer: Any exercise that simulates like crunching exercise will do. You lay down on your back, and bend your knees and hips up, and now you raise your head and chest. There is different version of the same exercise. Can do a set of thirty a day.