Hi! This question is for Julie...I just bought my son a Britax Parkway (after reading all of your recommendations on this board), and he loves his new "big boy" seat! =) He's 41 inches tall and 40 lbs. My question is: Is it safe to lock the seat belt when strapping him in? By that I mean pulling the seatbelt all the way out, and then letting it retract until it "locks" him in the booster? My husband and I have differing opinions and we could really use your advice. Thank you!