Is anyone elses baby not sitting

Cherie

My baby girl was born at 37weeks induced due to IUGR, which means she stopped growing. She was 2.2kg when born and should have.had NICU time but we had a 4day hospital stay instead, she had her weight drop after birth to 1.7kg.m and then has been steadily gaining weight. She rolls, comando crawls however she isnt sitting.yet at almost 9 months she is behind my other children by a few months already..... any one else have this issue ??