I have the Kindle 2, and love the 3G for buying books when I'm out and about. I just bought my husband a Kindle for his birthday, and I did not pay for him to have 3g on his. When I asked him if it was important to him, he reminded me that his phone can be a hotspot. He always has his phone with him, so he already has 24/7 wi-fi access.
As far as kids books - how old is the kid? Are you reading out loud, or are they reading independently?
Enjoy your new Kindle!