As long as their able to lift and hold their head up it should be fine. Which at 9 months most babies can

I've used a blanket and a shirt once for my scent to be close to him. He is able to lift his head and turn it, pull the covers and everything. His pediatrician said he is fine. I did it because he was sleeping in our bed since his birth and his mattress was not soft at all.

My little one got used to our bed and her crib mattress sucks so I have a blanket on top of the sheet. I know it's a risk but she's rolls no problems s sleeps on her belly or side now so I'm as worried. Not to mention even though this scared me half to death when she was little, she covers her face with her favie blankie. She's strong enough to lift pillows and remove the pillow covers and take the blanket off when she's hot. It's your choice mama. We know our kids

Is it a breathable material?