Rifles stored in a six year olds room?

My stepson told me his mom and boyfriends rifles are stored under his bed. He also told me they both have handguns in the house and where they are located. He has also told me they take him to the bowling alley for their league games and while there they drink and then load him up and drive him home. The money that we pay to support him every month is not used for him, when we picked him up last week his jeans were too small and he was wearing shoes he's had for over 2 years. My heart is breaking for him because he would be taken care of with us. We don't have an extra 5k sitting around to fight for custody. We have 3 daughters living in our home but he has his own room here. I'm debating on getting CPS involved. If they take him we can pass all of the requirements to gain custody, I just don't want it to fall through the cracks and how can we prove the neglect. I'm in Harris County, TX