Hi Aquila,
I reference two previous posts on this forum:
MRI template for children
MRI template for Children (4-7 years)
If you want to see what kind of differences you may observe with different head sizes: create two subjects, one with the 1yr template and one with the default ICBM152 template. Import the same recordings and compute the sources in both subjects, compare the results.
Cheers,
Francois