This used to happen to me too. I realized it was because my kid couldn't sit still and was bored. It doesn't take much movement if they can find the right rythm to really get it shaking back and forth.

I'll also say that after about 2 years of consistent use, one of the wheels simply fell off my Burley trailer. It was like Ron White, "It fell off, the wheel fell off, it fell the $%&* off." You might check the integrity of everything, but three years of daily use is a pretty solid amount of time for them to last.