Yes, Bon départ 2 may have a different composition than Bon départ 1, including varying amounts of ingredients like calcium and iron. It is possible that the preparation 2 may require more effort for the digestive system to break down. It is important to monitor your child's tolerance to the new formula for at least 2 weeks after switching. Some discomfort or constipation could be caused by the iron supplements, but it can also be due to other ingredients in the formula. Overall, it is a learning process for your child's digestive system to adapt to these new foods, which may come with some challenges at times.