The baby trailer made me think of this. It's apparently not advised to take infants on bikes or bike trailers. Something about the neck muscles not being fully developed and the skull plates not yet fused. I'm not a parent, so I don't know the details. It's worthy of investigation though.
There's a young dad who used to bring his daugher to the library where I work P/T, towing his daugher in their Chariot bike trailer. One day a couple of weeks ago he arrived by minivan. I was shocked, and asked why. He had his infant son in a carrier and explained it to me. More disappointed than either of us, was his daughter. She loves the Chariot but dad won't be riding for a year. Had a little resentment going there against her baby bro' for that.