From about 1 month our wee lad was out in the trailer. We used a standard cheapo trailer from eBay with a cradle for his Maxicosi Cabriofix infant car seat. The seat locked into place and the cradle was isolated via vibration isolating mounts. He notched many miles, mainly asleep. We rolled it once clipping a tree-stump. He woke up.
At about one year he moved onto a Bobike Mini, which he absolutely loves. It is important for your little one to be able to hold their head up and for more off-road stuff, to be able to anticipate bumps. I always say “Bumps” and our wee lad is ready. We’ve ridden widely, including Caddon Bank.
Number 2 arrived on Tuesday, and will be out in the trailer soon. A secure seat in a trailer with the vibration isolating maounts and soft tyres must be more comfy than his pram.