You mean you bolus NS...right?
For everyone's education - the basis for doing 1/4 or 1/3NS is due to the estimated range of Na being 2-4 mEq/kg/day. On the lower end of things, at 20kg, you're closer to 1/4NS, while at the upper end of the range, you're at 1/2 NS. As far as I know, there are no studies showing a benefit to using hypotonic solutions. The Peds Nephrologists will still discuss the appropriateness of using hypotonic fluids, but practically...it's a moot point. In the NICU, the babies are going to be on TPN within 24 hours with precisely controlled levels of sodium, and if you've made it home and then come into the ED sick, you're going to get resuscitated with NS, and on the floor, likely going to get D5 1/2NS...