Not very strict. There was more of an unspoken "understanding" between us kids and them that we wouldn't do "bad" things, or that we'd join the ministry school, or that we wouldn't date unbelievers. But when I was a kid (8-13) I was allowed to play sports with neighborhood kids and if my parents met theirs I could even go to their houses to play. I could always tell my dad regretted not celebrating holidays and birthdays, and had a love of sports - we'd play basketball or football all the time and he'd show me patterns and moves. My parents never disallowed worldly kids to come to our house to play. My dad to this day regrets raising us as JWs (right dad? he reads this board) but I tell him he wasn't so bad and only did what he thought was right and what else can a person do?
edit to add: yes, no water guns or cowboys and indians, and no organized after school activities. My dad didn't like hearing "jeez" or "holy moses" and expected our behavior to be good so as to maintain our reputation. All in all not too bad. We always watched the Smurfs or "violent" cartoons of the early '80s (Wondercats and Transformers anyone?). They never browbeat us to go out in field service. I can see now how tough it was being a parent, making all those decisions and worrying all those worries, and I could never do it. I give my parents, to this very day, all the credit and love in the world.