There is nothing specific in the current Texas family code that allows grandparents to have summer vacation time with the children. However, it you are petitioning for grandparents' rights in order to get access to your grandchildren, you may be able to ask for a certain amount of time in the summer as part of the visitation arrangement.
Any case involving grandparents' rights can be very challenging. The courts usually recognize the parents' right to socialize their children as they wish, even if this means prohibiting the grandparents from having access to the children. However, in some situations, such as a divorce or death of one parent, the grandparents may be able to petition for court-ordered access if they can show that it would be in the best interests of the children.
It's important to understand here, however, that the mere fact of spending time with their grandparents as a positive is not likely to be enough for the courts to override the parent's wishes. You will generally need to show that you have an established relationship with the children and that not seeing you is damaging to the child. Grandparents who have been primary caretakers of the children, such as when a parent is incarcerated or deployed, are usually in the best position for these types of cases.
It's normal to be upset about not getting to see your grandchildren, particularly if you feel that there is no reason for the lack of access. However, it's important that you understand your rights and options before taking any legal action.
Source: Texas State Law Library, "Texas Family Code Sec. 153.001," accessed June 09, 2016