Growth & Development:
Adequate DHA during breastfeeding is a good indicator that it was adequate during pregnancy, as well. This has been shown to support improved birthweight and lower the risk of prematurity, in areas where omega-3 intake is low .
Cognition & Behaviour:
Arguably the most important benefit for baby is the continued absorption of DHA into the brain , as it grows and starts to activate learning, memory and body control after birth. Infants breastfed on milk with higher omega-3 content have recently been found to have improved temperament , including fewer negative reactions. They have also been reported to have a 5-7 point improvement in IQ as toddlers 
Eye health and vision:
Visual actuity, which is another word to describe sharpness of vision, has been found to improve in babies whose mum’s breastmilk contained higher DHA levels  . Higher DHA in breastmilk is also related to a protective effect against developing eye problems, such as damage in the light sensitive part of the eye (retina) .
There is collective evidence of an improvement in immune system function, and a lower risk of developing allergies and asthma in the first few years . This benefit may also extend to preventing appetite losses in infants during illnesses, such as lung infections .
Emerging evidence even shows a possible link between breastmilk omega-3 content and gut function later in life. In research models, lower levels of omega-3 in mum’s milk were related to altered gut microbiomes, similar to those seen in gut infections and obesity .