8 months old.

You may or may not have heard of migrating partial seizures of infancy (Epilepsy of infancy with migrating focal seizures). One of the characteristic features of these seizures are runs of alpha frequency discharges over the hemispheres, migrating from the one side to the other. This may cross your mind when you see the following EEG

There is another example

Here is a third example:

And here is a fourth example:

Fear not, this child has no EEG evidence of this nasty syndrome. The above are normal sleep spindles in a child of this age, longer in duration than in adults and teenagers and typically appearing in an alternative manner over the two hemispheres. These pages represent "beautifully normal' rhythms in a child of this age (pardon the terminology, but hopefully you get the point).