I can't quite gauge his size. He certainly doesn't look like the poorly little baby that he used to be, all skinny and scrawny......but then if we're to believe that he's wearing aged 3-6m clothes and a lot of those look too big, then what's that all about? TBH I usually believe opposite of what she says, so he probably has caught up a bit, weight-wise, but I wouldn't say he's overly chubby or big for his age.
I do agree about his development being behind in other respects though (their fault, no doubt) but thankfully he appears to be becoming more mobile and is hopefully finding his voice as well.