Using ACS Estimates as Denominators for Rates and CIs

I'm new to ACS and trying to use state estimates as denominators to estimate rates with confidence intervals over time, specifically for under 5 years by race.  I found the necessary population estimates but they provide an estimate and error for the total population and a percentage and error for the <5 population.  The data I'm using for numerators is complete data and while I have calculated rates with CIs for estimated numerators, I have not calculated them using a denominator with error before.  Does anyone have a recommendation for how to do this?  Or a place to look for the methodology?