Would this lens be a good fit for me?

I have a Nikon D3100. Currently, I use my camera to take portraits of people/families in outdoor settings. Is this a good option for me? If not, what would other choices be that are comparable in price? Thank you!

It would be a fine addition to the 18-55mm lens that I assume you already have. On the short end you can do portraits and it will give some reach for sports or anything else you may need it for.

Get a fast prime, no need for telephotos for those needs.

Absolutely superb, grab it with both hands.

Well it's not a prime lens but for that low price I think you can have big bang out of it.
If you like doing portraits you should take a look at the Nikon 50mm 1.8G & 85mm 1.8G