Osaka-Kyoto-Tokyo

Hi,
I am flying into Osaka then travelling straight to Kyoto. I'll spend 4 days there including a trip to Nara. From Kyoto I'll take the Shinkansen to Tokyo where I'll stay for 7 days then leave from Narita and fly back home.

• Is it better to get a JR pass or buy all the tickets separately?
• If I don't use the JR pass is there any other kind of pass I can use in Kyoto or Tokyo to save time at stations as I'll be travelling with my two young sons.
• If I don't have a JR pass do I need to book the seats ahead for the Shinkansen from Kyoto to Tokyo? And if so can I do that before I arrive in Japan?

Thanks for your help.