Yes. My son just made 3 months yesterday and for the past 2 weeks when he is laying down he tries to sit up. It looks so funny to me. It looks like he is doing crunches. I make jokes saying he is tring to get his six pack ready : ). But yes, he would rather sit up straight rather than be held like a little baby. It's hard to let go of that cause it means the are growing up and you want them to stay little forever. But I think it is ok to sit them in a sitting position because it is getting there back muscles stonger. Just like when you put the baby down for tummy time, it is helping them get thier neck muscles stronger. I sometimes even prop him in a sitting position on the couch when i'm right there next to him.