As is probably true for most of Texas, Houston weather can change very rapidly at certain times of the year. It's a good idea to look at the weather forecast to make sure the weather's plans go along with your vacation plans!
Houston has a humid subtropical climate. I think there needs to be an emphasis on "humid" because at certain times of the year it can be very humid.
Summers in Houston are quite hot, with temperatures averaging around 94°F in July and August. Winters are mild, with temperatures averaging around 45°F in December and January. The wettest month is usually May, with an average rainfall of around 5½ inches.
Since Houston is so close to the Gulf of Mexico, there is usually a big chance of hurricanes and tropical storms every hurricane season, which typically is from May to November. There is usually plenty of warning when these storms approach though.
Here's a complete weather forecast for Houston for the next several days:
(Note: For some links inside the weather forecast to open, you may need to enable pop-ups for www.fun-things-texas.com in your browser. AccuWeather® also requires that cookies be enabled.)
I hope Houston's weather will play along to give you and your family a great vacation in Houston!