Hi Anna, your son is experiencing what is commonly referred to as secondary nocturnal enuresis – a term which is used to describe the condition where a child has been dry at night for 6 months or more then begins to wet again. There are two main causes of secondary bedwetting: psychological and physical. While medical causes are rare it is always important to rule these out first by making an appointment with your GP so that he/she can run a few tests. The birth of a sibling can cause significant stress among young children. Despite parents every effort to include the older sibling, children can feel that they have somehow been replaced by the baby and may be unsure of their new role in the family. This is a time when your son needs lots of affection and reassurance. Set some time aside for some special one-on-one time where he does not need to share your attention. If stress is a contributing factor then children often stop wetting after they feel more settled and their routine returns to normal. All the best and congratulations on the birth of your new baby!