I jsut re-read your post, in particular the last sentence, "... I need to get great pictures of my kids."
The lens choice to a great extent depends on the age of the kids. if they're very young - from toddlers up to about 7 years old, they're perpetual motion machines. Nothing short of a 50mm AF-S f/1.4 is going to be able to help freeze the motion most of the time. Past the age of 7 (approximately), so many kids are engaged in field sports, swimming, gymnastics and after-school indoor team sports that the 50mm remains in the bag and you instead need at least a 70-300 to help isolate them in action from 50' away.