I'm a personal trainer fyi :)

Well congrats on your little one!!!!!
I'd start just walking. At least 30 minutes every day for at least 3 weeks. You need to let your body heal first. After that just start a very simple program of light weight lifting, combined with keeping the walking going. Once you start to feel stronger you can up your weightlifting and really get into a program. Start slow though, childbirth is killer hard on your body and even your abs need time to heal!!! Here is a simple full body routine I posted earlier, I've found it's super effective to get started and motivated cause I's simple, easy and short.

Push-ups, start with wall Push-ups then knee Push-ups when those get too easy, squats-normal ones and plié squats and lunges (hold on to a chair with one hand if the lunges throw you off balance at first), lay on your back and arch up into a bridge for your butt, lay on our back and do leg lifts for abs. Start with that. Also look up dead lifts on YouTube. Those are AMAZING and work your hamstrings which are hard to target and important for runners, as well as your back. You can do them with just body weight, just look at YouTube for the form which is important or hold a can of soup in each hand