My 5yo is almost 6, but he's always been fearless (flying around on his Razor scooter since he was 3). His 3 1/2 year old sister simply assumes that anything he can do, she can do. It's amazing to see this in action - especially in the swimming pool, where they've both become far more advanced than their peers.

While their natural competitiveness leads to their individual progress, it also makes cooperation a challenge. I think the tandem trail-a-bike has been a great exercise in teamwork simply by requiring them to pedal together. It also puts them in a position to have a dialogue with each other instead of constantly battling for my attention.

I've struggled with their helmets. We have a assortment of them, but none stay level on their heads without an uncomfortably tight chin strap. I've been trying to make gradual adjustments to the straps and padding, but they obviously need work.