14-day in Japan - JRpass or not?

Hello,

We are 2 adults with 2 children (aged 0 and 2), travelling to Japan for 14 days, from February 28th to March 13th.

We are landing in Osaka in the morning, and leaving from Tokyo. Our plan is as follows:
Osaka - 2 nights
Nara - 2 nights
Kyoto - 3 nights
Hiroshima - 2 nights
Tokyo - 4 nights
Short stop at Himeji before travelling further to Hiroshima, and Miyajima island.

Would you recommend us buying a railway pass?
According to the prices of train tickets between the cities (not sure if correct prices I found on different websites), it might seem like the 14-day JRpass is not worth it. Do you agree?
If it is not worth buying a railway pass, is it possible to buy train tickets in advance (at least the shinkansen to Tokyo)?

Kind regards,
Tanja