There are some activities children are sure they can do without assistance, like roller-skating or riding a bicycle. This is very unlikely. These kinds of skills can only be learned through experience. There is virtually no way you can convince your child ahead of time she does not know how to roller-skate or ride a bicycle. She may have to find that out before she cooperates enough to let you help her.
First she must get on the bicycle or on the roller-skates and give it a try. When she finds she is unsuccessful, she may want nothing to do with the bicycle or roller-skates. your gentle support and encouragement usually gets her to try again, if you promise not to let her fall. You help her to maintain balance in her initial efforts to ride or skate. This works out fine for a little while. Now, let go and let her try it on her own, knowing she probably again goes some distance and falls. You cheerfully help, let her try it on her own, and then help again, with an ample supply of bumps and bruises being added along the way. After a while, she rides the bike and roller-skates on her own. Even then she likely becomes increasingly more daring and presses the limits of her abilities. Wrecks and falls again occur. By then, though, she can back off to where she is able to skillfully ride the bike or roller-skate, only occasionally having an accident.
Teaching children to cook, play ball, water ski, and swim follow this same pattern. It may be a long time before they are ready to participate in the activity as a pastime or simply for the pleasure of it. your role is teacher, consoler, and encourager - the voice reminding them not to ride so fast or recklessly, not to skate down steep hills, not to throw the ball toward the window, not to swim into deep water, and so on. You set and enforce the boundaries and limits even while helping your children learn about physical skills and activities.