Thanks everyone for all your help.
First of all - Hayden (black lab, just over a year old) has been on the same food since the beginning and it is the Iams Smart Puppy (yellow bag).
Jada (yellow lab, almost 2 yrs) is on the Eukanuba Lamb & Rice (pink bag). I am fairly ignorant about food-quality...so any suggestions are welcome! I was thinking Hayden should get off the puppy food, but the bag does say for up to 24 months. What are the thoughts on this?
There has been no recent changes in their diets or treats or anything like that. The only big change recently is that we just got Jada about 3 weeks ago now...and I know its a big change! I thought maybe Jada has always done this and Hayden learned it from her. However, Hayden spends a lot of time at his grandparents, and their Chocolate lab loves the stuff and Hayden has never followed his lead & adopted this behaviour...until now.
I do notice that they don't seem to take any interest in the "fresh stuff", it seems to be only the frozen stuff that they can dig up from under the snow.