The first or second week in April should be just about right, though this can vary from year to year. We were in Brenham and Fredericksburg last year during the second week of April and that was about right that year. We stayed at Artesian Park RV near Brenham. I would not rate this park very highly, but we have stayed there several times because of its location. Nothing highly negative, but certainly not a resort.
We spent most of our time in Fredericksburg. We always stay at the KOA out east of town. We do not usually seek out KOA parks, but this is one of our "regulars." I would think you would want to go on to Fredericksburg if you are in the Brenham area.
Brenham is the home of "Bluebell Ice Cream," and you can tour the factory. There are many worth while "sights" around Fredericksburg: The Wildseed Farm; Luckenbach, The Nemitz Museum, many German restaurants, and too much more for me to name in this response.
Hope you get to make the trip. It is the best time to come to Texas. I can also give you some good stops here in the Northeast part of the state. Just let me know if you are interested.