I think give it a little bit more time. But not too long.
I remember at 8 weeks DD1 was smiling & laughing & carrying on, then a little boy came over. She was all happy & laughing at him, & he, at 11 weeks just stared.
Obviously, 30 minutes out of someones life doesn't count for much, but to see the difference between the 2 was obvious. He had no facial expression at all, but he did look at her.
Maybe they should ask at their next MCN check up.