New Judge
Instagram is just an image sharing site which is popular because it's very easy to use it from your phone, and it gives you lots of filters and options to make yourself look nice in photos. If I upload a picture, my followers can see it, and I can also see pictures uploaded by people I follow. Most of it is just people taking pictures of their day out or their lunch or whatever, but I assume more than that goes on there. Never seen the point of it myself, but people clearly like it and it doesn't do any harm, so hey ho.
Anyway, all Beyonce has really done is post some very high-budget pictures to Instagram with her children - which, obviously, her followers can see. Essentially, she's just done what the point of the website is with some more polish. Media has picked up on it because journalism is dying and they tend to just regurgitate everything they find on the internet now.