What did Rachel mean when she stated that Hashem had judged her...?
Rashi: She meant that Hashem had initially judged her and found her guilty (which is why He withheld children from her), and had now judged her favorably and given her a son (via her maidservant).
Seforno: She acknowledged Hashem's righteousness in withholding from her children, and thanked Him for giving her a son 'a staff to guide her and a shovel to bury her'. 1
Targum Yonasan: He had now judged her mercifully, accepted her Tefilos and given her a son.
See Yevamos, 65b.
Why did Rachel and Le'ah refer to the children of Bilhah and Zilpah as sons, and not Avadim?
Seforno: Because they set their slaves Bilhah and Zilpah free when they offered them to Ya'akov. 1
רש"י: דנני אלוקים- דנני וחייבני וזכני: למה לא פירש שזה מלשון דין [-עונש] כמו בכל מקום?
גור אריה: לא היה כאן דין אלא זכות בלבד.