Wants to be fit by 40!

I'm 37 y/o and I'm decided to be my best at my 40's. And i just realized how hard it is!!
My goal is not to lose weight but get more toned and i never thought how hard that would be, i mean is it even possible???
I have 3 kids...is this only an excuse? maybe! but I know i am going to do this no matter what!