J.L.
Hi D. - My 8 year old was diagnosed with benign congenital hypotonia at about 8 months of age. She also had deformational plagiocephaly (flat head) and had to wear a helmet for a few months. They were testing her for CP along with craniosynostosis (early closure of the soft spots) and finally she was diagnosed with the hypotonia (which you probably know is low tone). She had lots of O/T and P/T through Birth to 3. She also had P/T through a private place that I paid for (rehab associates) and through the public school system after Birth to 3, which was I believe at age 4. Right now, you would never now she had low tone, with the exception of her cautiousness with climbing and she is still learning how to ride a two-wheeler. She also has a very slight speech impediment (we had sent her for speech therapy as well - she had low tone in her tongue when she was born). We didn't know the diagnosis until later but they had to teach her how to suck from a bottle as she was unable to get the milk she needed from me.
Your child/grandchild should maybe see a neurologist and go through those steps. Also, I highly recommend Birth to 3 if the child is within this age range. They are amazing!
Hope this information helps! Good luck . . .