extending axles?

I want to make my bot 4 wheel drive by adding a sprocket I'm using 100mm blue wheels do I need to extend the axle and if so how

bolt the sprocket onto the wheel :)

I understand that but would I do that

get the sprocket inline with the wheel and then drill 3 holes out and screw them together.

drill holes in wheel and sprocket and make sure they line up and the sprocket is in the centre and then use bolts to keep the sprockets there :)