Your baby's brain is mostly fat! The long-chain fatty acids DHA and AA are the most important ones for babies. DHA is an omega-3 fatty acid, and AA is an omega-6 fatty acid. Other omega 3's you'll see on food labels are EPA and the plant-based one: ALA. Apart from AA, there are other omega6's: LA and GLA.
LA and ALA can't be made by the body like the others can, but it remains important to take in enough of every