2 1/2 years is perfect in a child specific bike trailer. We have 4 kids. I think I remember reading 1 yr+ recommended. Started the first around 11months, then 10, then 8, then 6months for our youngest. We had Chariot trailers, both the highest end single and the Cougar double. Very nice child trailers, the Chariots. Plastic bubble seals up nicely for the colder, wetter commutes. Highly recommended. We also have a Burley Honey Bee double as our backup. Good trailer too but we preferred the Chariots. You can leave the trailer and/or WeeHoo/TrailABike tagalongs at your child's preschool/school and then ride unloaded to work. Hook it back up or switch off with your partner in the afternoon.
We started our youngest at 2 1/2 years on the recumbent tandem setup, the WeeHoo IGo. It has small panniers, chair with harness, handles, drink holders, well made, etc. Kiddo can even nap while riding. We put thousands of miles on the WeeHoo, including self contained touring over 485 miles on one of our family trips. Near daily use commuting through Austin, Tx. We then switched to an Adams TrailABike around 4 with all of the kiddos. Outfitted with rear racks, panniers, fender. Even pulled a TrailABike with the Chariot or the Burley behind. Long train. Now I converted the Burley Honey Bee double to use for our Redbone Coonhound. Our youngest, now 5 and 7 yrs, ride behind me every day on our Bike Friday Triple tandem setup for commuting/touring. Have fun, ride big on the streets, use bike facilities when/where you can, stay safe !