Tandem bike attachments are perfectly safe as long as you fit them and operate them according to the manufacturers’ instructions. It is important that you adhere to the age and weight recommendations because these are there for a reason! If a very heavy child uses a tandem bike attachment, they could easily throw the adult bike rider off balance and this is very dangerous.
It is also important that you child understands that they must hold on and put their feet on the pedals. Children who are aged less than four are unlikely to follow these instructions reliably.
The bike attachments are designed with your child’s safety in mind. The handlebars and seat are usually adjustable so that your little one can sit in a stable position. The moving parts are often guarded away and there is often a safety flag.