Squat Jumps are great for this. Your thighs have the largest group of muscles in them (the quads- 4 muscles grouped together). Squat down till your thighs are parallel to the floor. Sit back into the squat, so you are putting the weight in your heels. This will keep you from letting your knees go over your toes, so your knees don't get too much work. Then spring up as high as you can. Remember to land lightly with knees bent again. Repeat ten more times.
Push-Ups are another power move that uses every muscle in your upper body and your core. If you can, try to do them on your toes but if your form is better on your knees, that is fine. Bad form, would be letting your back sway down towards the floor. Keep your abs held in tight and that should solve the problem.
Arabella is supervising my form right here. I am waiting for her to show up to her play dates and start instructing her friends to do lunges and crunches. She already thinks you are suppose to cheer and clap for someone, every time you count to ten, because that is what we do for my clients!
One of the best, and my most favorite, stress reliever is dancing. Add in there, one precious child and laughing, and how can you not have fun? We just turn the music up loud, act silly and move to the beat!