Basically, follow the Division of Responsibility. Regular readers know that with feeding this means your job as a parent is to provide what, when and where the child eats, the child then decides if and how much.
The same should be true for activity. The parent's job is to provide the opportunity for physical activity, the structure and support and then leave it up to the child. The more you push, the more they will resist.
It's been fascinating for me to watch my own case study, now almost 4. Her innate level of activity has jumped recently. She seems to go through cycles– very active as a crawler and toddler, a little less so around 2-3, now more active again. We went to the sculpture garden recently and she ran the whole time (photo top.) She had endless interest in hide-and-seek, ran across the bridge to Loring Park to the playground. A few months ago she would have been riding in the stroller. She runs around the house in angel wings, starts spontaneous games of bowling with cups and materials scavenged from the recycling bin, jumps on our second-handjogging trampoline, launches herself into piles of beanbags etc... I sometime wish she could sit still for all of Finding Nemo, but I can't force her to watch TV either, no matter how much I could use the break!
Tips for supporting activity:
1) Don't push it, allow them to find their natural rhythm.
2) NO TVs in the bedroom, limit TV watching to what feels right for you, but no more than 2 hours (for some folks it might be none, or 20 minutes...)
2) Make a point of being active in a fun way, ride bikes to the park, set up indoor obstacle courses (we actually had no furniture in half our living room when she was little so she could run and jump on couch cushions) indoor bowling, velcro darts...
3) Find something they like to do and sign up for a class. Rec centers are great for this. Be careful not to over-program your kids to the point that you miss out on Family Dinners regularly.
4) Go for Winter lights walks. Bundle up after dark, bring a flashlight or glowstick ($1 for a bunch at Michaels) Even if you have to bring them in the stroller or wagon for awhile, get in the habit of moving your bodies in a fun way together.
5) Make a list of scavenger items for a walk, Snelling State Park is full of deer and wild turkey. We almost always see them! (Ask them to collect pine-cones, a tiny rock, a feather...)
6) Make your own fitness about having fun and feeling good, if weight loss is your goal, you are less likely to enjoy yourself and continue with the activity.
7) Play music with a great beat, and dance with them
8) Be positive, telling a child they are fat or need to lose weight is the best way to get them to be LESS active. Don't talk about weight at all.