You gotta wake your kids up with a smile and keep things happy. Shouting at them will just put both of you in a bad mood.
I open the curtains smiling and jokily, waking up the kids with a smile on their faces. Even if they are grumpy, keep on being happy and smiley.
if they insists on staying in bed, take the covers off them and stand them up, still joking and saying funny stuff.
It works!