Welcome! For your situation, I'd recommend getting into some flash work. This way, you get to bump up your shutter speeds whilst lowering your ISO. Learn techniques like fill-flashing and 'dragging the shutter' which will all give you the potential to make flash photography look more natural. Aim for an external flash unit such as the 430EX or 580EX II, and you'll really be kicking along.
As for what you're doing now, notching up the ISO is a good start. To aid the situation, turn that f/ number down as far as it will go, if you still don't have enough light. Be aware that that the f/ number (which controls aperture size) is a creative tool, which also affects the depth of field of focus. So the lower the number, the higher the 'background blur'. This is one way to isolate your subject (such as your son) from the background. Learn about the 1/focal length rule for shutter speed (which gives you a rough indication of how fast the shutter speed has to be to guarantee a shot reasonably free of image blur caused by hand shake).