Should be fine with what you are describing, I only struggle with mine when my 2 year old is running around, but heck, I have troubles focusing the little one even with a Canon 7D.
BTW PM an offer and I might sell you my X100 , maybe the X100s will focus correctly on my child lol.
Oh I don't want to insult you as I don't shoot as much as I'd like but the 35mm focal length is perfect for me but I'd rather wait to see agreeable prices on the used market. I'm hoping they will steer toward $500 soon but that may be naive of me.