MagPi has some robotics but it's not really dedicated to it. It depends on how deep you want to get. The Lego Mindstorm/Vex are great kits for kids and robotics. As an adult or doing more complex robotics, I would look at tutorials for Raspberry Pi or Arduino.
Make is another good magazine but it does not have a free edition.
You can also check out @makerhacks free robotics course:
https://learn.makerhacks.com/