Hi there! My kids are now in their teens, but I can definitely relate to your dilemma. There were times in my life where I thought there was no way I could fit a workout into my busy schedule. The fact that you're walking in the morning is a great start. Make sure you walk quickly, maybe even working up to a light jog for a minute or two, then going back to a walk to get your heart rate up.
Sometimes it's easier to break up your workout routine into smaller increments throughout the day while your little ones are napping or watching a kids show.
If you happen to have an "old-fashioned" VHS player, "Abs of Steel" has a workout tape of three 10-minute ab workouts that are really good. They're fairly inexpensive too, since they are on VHS. You could easily fit one ab routine in during a daily naptime.
I just wrote a blog titled "
But I'm Too Busy To Workout." If you're interested, you can check it out.
Good luck to you!