I bought a batch of fem white widow and been growing for the last 4-5 weeks and some seem like start to flower? 
That does look like it is starting to flower. I assume you are still giving them about 18 hours of light per day? Did these plants get stressed at all? Is there anything that might be different in their pots? Hand feeding a bunch of different containers can mean each plant is getting a little something different. If it is just a pre-flower, there is nothing to worry about. If somehow you got something with autoflower genetics, there is probably nothing to worry about, harvest when ready as determined by the trichomes.
Ok Thanks. Just 6 out of over 40 got flower. I have 18/6 schedule.