My sister has 3 kids. The eldest and the middle child are 1 year & 9 months apart, and there is 2 years & 2 months between the middle and the youngest. The elder girl really played up when her first sibling was born, she even got kicked out of daycare for biting & other attention seeking behaviours. But now that the new baby has come along the older 2 just play with each other and there doesnt seem to be any jealousy from either of them as they still have each others company.