How do I sleep train my baby and let my baby sleep longer at night ?

How old is your baby? I suggest to help your baby differentiate day and night. During the day, be more active, play and talk to your baby a lot. At night, be more calm, no more active plays rather you can opt to play soothing sounds or lullabies. We have dim light and seems like a signal to my baby when I switch off our main light and use dim light instead, she knows it's sleeping time. We do this every night, and we co-sleep which I believe also help my baby to feel secure and sleep peacefully at night.

Get baby to wake up at around the same time every morning and put baby down for naps at the same times each day. Set a clear boundary between day and night so baby will associate the night with sleep. If baby's daytime routines are active, keep his bedtime routine as calm and quiet as possible. My friend would actually nurse her baby when the child is on the verge of sleeping instead of before. This helps her baby sleep longer at night.

try use fresh aloe vera, cut into small pcs after shower use to to wipe ech allergy area. 1 pc 1 area do no reuse.. quite effect for my nephew.. he also uses california baby cream

babies under 6 m.o. need to wake up every 2-3 hours for BF/formula. then you can gradually train him/her sleep longer at night after they have solid food.