Many people will balk at the word 'exercise'. However, being physically active does not always mean it has to be hard work, just regular. When starting any new physical activity, it is always advisable to begin with short, gentle sessions and build up gradually from there. Often, once you get into a pattern, the activity becomes easier and more enjoyable (and even something you may look forward to!)
You may find that if you can talk your partner (or a friend) into exercising with you, then the commitment to the other person becomes a great help in actually doing the exercise regularly. Finding time in a busy life schedule can also be a barrier to overcome. Try and be creative with your physical activity and perhaps plan some social gatherings around activities that require some physical input, such as bush walking or bicycle riding. If you have another child, then scheduling your exercise when your partner is home, or organising a babysitter, or perhaps attending an organised activity with childminding facilities, may require some research and planning.
How often, and how long, you exercise will be very individual. Being physically active everyday is ideal, but not always achievable. Every second day is excellent, 3 times a week is a very good, once or twice a week is consistent (and the odd occasion or whenever you get around to it is better than nothing!) Aim to be active for at least 20 minutes at each session, 30 to 45 minutes if you can.