With the cost of fish and the mercury problem there should be other ways to get this important supplement.
For a complete discussion on alpha 3's and why they are so important see letswakeupfolks.blogspot.com and the article Just How Important is Fish Oil (alpha 3 Omega Acid) to our health?.
The omega-3 used in brain development is DHA, which is why the advice to eat fish is offered to pregnant women. Chia and hemp have ALA, not DHA. The body converts ALA to DHA at a rate of about 5%, so you would have to eat a rather large amount of those seeds to (maybe) get the same DHA content found in a piece of wild salmon. ALA may have some benefits of its own WRT cardiovascular health, but DHA is brain food, EPA is mood food, and both are mostly found in fish.