My kids are 18 months apart and we've never had any problems with jealousy. We started preparing my daughter for the arrival of her baby brother pretty early on. She had always loved babies and was always very interested in them. I explained that I had a baby in my tummy and I encouraged her to talk to/tickle/blow raspberries on the baby. She loved that she got to play with him before he was born. We also got her some baby dolls and helped her play with them gently. She enjoyed pushing them in their stroller, rocking them, putting them to bed, etc. We even set up the crib, swing, bouncy chair, etc. early so that she could get used to all the new stuff. She would put her babies in the swing our bouncy chair to play. When my son was born she got to spend one night in the hospital with us so that she could understand that he was a new member of our family. That made it easier on her than just bringing a new baby home out of nowhere. Once he was home she would take care of her babies while I took care of her brother. All the "training" that we did with her made her very excited to finally meet our new baby. She was always happy to bring us blankets or pacifiers when we needed one and she would help us in any way she could.Now that I'm pregnant with our third baby our daughter is very excited once again and we're trying to get our son involved too. He's not as mature as our daughter was but he still like blowing raspberries on my tummy and we're keeping him as involved as we can.