The optimal balance of DHA and ARA intake during infancy is still not known, but current best practice suggests that the amount of DHA in infant formula should not exceed the amount of ARA.
Link to Publication: http://www.sciencedirect.com/science/article/pii/S0065310116300111
Carlson SE, Colombo J. Docosahexaenoic acid and arachidonic acid nutrition in early development. Advances in Pediatrics. 2016;63:453-471.