Sidecars, apparently very difficult to set up.
With a baby born in August could not face the thought of time off bike. At 3 weeks he was in a trailer, padded and adapted with pillows.
Trailer was great on flat roads but very hard, like towing a dead weight up hill. We also managed quite a bit of Rough Stuff with it.
Following Easter, as soon as he could reasonably sit up, he was in a bike seat, however he was in and out of trailer for a couple of weeks due to bad weather.
Plenty of layers and baby blanket wrapped around him. Managed to get a "buggy" cover/cape. A waterproof hooded item with hooks and elastic that fitted over child and seat.
Bike seat was rear type and helps give wind protection to child from parent.
Both walking or cycling keeping extremeities warm was the worst/most difficult bit. Even cut up a fur lined/quilted pram cover and made mittens and still he got cold hands.
For next couple of winters he returned to trailer for colder days, then joy of joy at 31/2 he progressed to tandem, now he can solo!
Do remember when progressing to tandem, their work rate is not effective in keeping warm and being further behind you do not have the same wind protection.
Most of all enjoy the sheer pleasure of getting them out in fresh air, and showing them the wonders of the countryside, but be prepared to be looking forward to a nice picnic rest and find off-spring wants to be pushed on swings or play with a ball etc!!