How to tell if myoclonic jerks are a seizure my child has these all through the night some nights but how to tell what's normal from myoclonic epileps?

Neurologist? As a physician it is through the descriptions that the patient makes that one can start to determine if they are meaningful. I would video these movements that you have concerns about and show them to your physician or pediatric neurologist. This would be very helpful and then if necessary further tests can be done to determine if they are seizures.