TELL them how active you are.
My sister in her late 50s is a nanny after retiring from a career as an elementary school teacher. She spends her spare time training for and participating in triathlons. She has current CPR and First Aid. She has a Masters in Educational Psychology.
She wouldn't dream of taking a position where the employers are uninterested in lots of physical activity for the kids. Potential employers were beating down the door to hire her.
Of course, some employers are really just looking for a cheap babysitter and house cleaner.