Most US hotels won't care. My brother has 3 kids and they always stayed in one room. Hotels outside of US are much more strict on this, and they will either insist on 2 rooms and charge you per extra person after 2.
That's why I like Embassy Suites and Homewood Suites since kids do not mind sleeping on sofa bed and when 4 or 5 of you showing up at the buffet breakfast, no one will say a thing and no breakfast coupons needed.