How much does your DS weigh? At 8 weeks DD was still a fair bit below the minimum weight for BGs (and probably Greenkids also), she is a little one though. If your boy is on the small side he might just be a bit small for them. Either that or the elastic may have stretched a bit over your DDs legs. I think on the internet somewhere there are instructions for replacing the leg elastic on BGs? I think it was originally done for the old (V2.0??) ones that had dud elastic, but I can't see why the same instructions wouldn't be useful in this instance?