I have two kids at home, ages 5 and 7, so the idea of a child of 5 speaking any language "as well as most natives" strikes me as wrong, even before we add in specialties (effective level of six!).
Given how much I need to explain to both of them, and how even their higher pitched voices make them more difficult to understand, I would rate them as no more than a 4 (with specialty), with additional fluency coming in later years.
This goes hand in hand with my desire to incentivize investing xp in languages, area lore and people interactive skills (and less put into core skills such as weapon, craft and arcane abilities). If we lower the requirement of Speak Native Language to a 4, we can shift 25 xp into other skills (still subject to early childhood limits) to round out the character. If a cap of 3 is chosen, this increases the shift to 45 points.
Don't forget, this would normally be language+com, and they have a -4 penalty on com at age 6-7, a -3 from 8-9, -2 from 10-11 and -1 from 12-13, so they don't really speak like a native until age 14, unless they have a naturally above average com score.
Actually, surprisingly realistic considering that I think I can understand my children just fine, but friends come over and have a hard time understanding them. Same goes for other young children - their little chirping voices with sometimes lousy pronunciation really can be difficult to grasp!
