Thanks for the insight Sarah. I have noticed that my second son responds to our BBC audio recording of Thomas and Friends in the car - my older son liked to listen to it so we played it quite a lot while I was pregnant. I also find that my younger son seems more mellow and easy going compared to my older son and someone asked if I felt more relaxed during my second pregnancy and I have to agree that I was more relaxed with no.2 compared with the first pregnancy.
In fact, I think my younger son responds to sounds a lot more than my older son did when he was this age. I was often alone during my first pregnancy and I'm afraid I didn't really talk or sing much. By virtue of the fact that I had a toddler during the second pregnancy, there was always a lot of chatter and singing. So a lot of what you've said is falling into place. Thank you.