Gf3 - best lens for indoor shots with fast moving toddler?

Having 2 fast moving toddlers myself I'd say the 25mm f1.4 is your best option (assuming you don't want to use flash). I have the 14mm, 20mm, 25mm and 45mm but in low light you need the brightest lens you can get and that would be the 25mm f1.4 (I don't count the f0.95 as it's manual focus, not really practical with a toddler). Even at f1.4 you're going to struggle though. You'll probably be at ISO 1600 or so and you may still struggle for shutter speed.