My son's gone to Nursery 3 days a week and other odd weekend rides since he was 8/9 months old, he's reclined and well strapped in, in a Croozer trailer with a baby head support.
he was sitting well holding his head and pulling himself up to sitting and standing.
yep take it easy and the roads\tracks do bounce 'em about way more than you or I notice on a bike.
he's a year old now as of last week and he loves being in his buggy and sleeps quite comfortably a lot of the time.
your the parents you know your little one and I'm sure you'd do nothing you weren't comfortable was ok