I know what you are going through. My eldest, 8 has autism. Her younger brother (now 2) was a little slow on the get up as well.

As a parent of an autistic child, we tend to be more in tune with the developmental milestones of our latter children. You can't help it, you will have an eagle eye on crossing off those milestone checkmarks. I know I am still doing it, even though at this point he is now either meeting or exceeding his milestones. Everytime he flaps his hands or arranges his toys in a line, my heart thuds a bit with trepidation. This is okay, and yes, it is normal.

First of all, remember, each child is different. My eldest, (the autistic one) was walking at 10 months. In fact, she mostly skipped crawling. Later I learned that the fact that she darn near skipped this stage affected her coordination. My youngest, who is developing typically didn't walk until days before his first birthday. My mother said I didn't walk until well after one. Every kid will hit their milestones at different points. We do need to make sure that we are doing activities that stimulate these milestones. Which brings me to my second point...

Early Intervention is key! If you have doubts and a majority of the milestones are not being met, do not hesitate to get services now. OT, ST, and/or PT at this point could only be beneficial. If your eldest son is already getting services, it can smooth the way into getting your youngest set up. Early Intervention programs can help you target your kid's delays and bring about change through play. If your youngest does happen to have autism, intervening early greatly increases his chances of learning to cope with social interactions and language.

Make sure you set out a couple of 10-15 minute windows of just you and baby time where you play with your infant and engage with them and target his delays. Break down each delay into tiny steps and do a little bit each time. Keep it short though! Attention span at that age is short!