Biking with kids update
I just realized the solution to wanting to tow Patrick & carry Ian on my bike at the same time is to replace our existing cheap rear toddler seat with a front mount seat. I've already ordered an i-Bert front child seat which, if it fits with me & my bike, means I can use a Trail Gator to tow Patrick's existing bike; provided I also switch out his current training wheels for flippable ones.