Vacation for Summer Graduate Research Assistantship First year PhD student here, in Computer Science

I will mostly likely be on a research assistant ship this summer. Is it too much to assume I will be able to take two 1-week vacations at different points during the summer? As a graduate student with a family, my family time is very important to me.

I know the answer to this will likely be "ask your advisor," so my follow-up question to that is: how do I talk to my advisor about this without seeming like I am lazy and don't want to work?
Two one-week vacations during a calendar year is completely reasonable.

That said, it's possible you work for an advisor who would find this lazy. In my opinion, that makes them an insensitive jerk, but my opinion won't help you graduate no matter how many times you link to this post.

I really don't think this is something you should need to "explain" to a human advisor. Give them warning, let them know your plans, be flexible where flexibility is possible and firm where it is not.

I asked in a comment about funding - it might be more complicated if you have different funding sources throughout the year (for example, if you teach fall/spring and have an RA for the summer). I still think a reasonable advisor should consider that you are working year-round regardless of funding and give you a break, but it might be a harder sell if your RA is summer only to take two weeks. In that case, I would just suggest to be reasonable - if the summer RA is the same kind of work as what you do during the rest of the year, it shouldn't really be an issue. If you are doing different work as an RA (which is quite common outside STEM but shouldn't be common in CS...) than your normal year-round research work, then I think you should either try to align your vacation with other breaks that are available during the rest of the year or work out an informal arrangement that is fair to you and your funder.