While your question, as asked, is a worthy one, you certainly understand that the more important issue in regard to your son’s religious observance is the long-term prospects. However, we will start with the question you posed.
Giving someone an object that is expected to lead him to sin violates the Torah prohibition of “putting a stumbling block before the blind.”[1] This applies to spiritual as well as physical “stumbling blocks.”[2] Poskim discuss giving a person an object that is not forbidden per se but which he will use both in a permitted and a forbidden manner. See, for example, Igrot Moshe’s[3] discussion of why it is permitted to rent an apartment to a mechallel Shabbat, who will use it for, among other things, matters that are forbidden on Shabbat.
In-depth analysis of this topic is beyond our present scope. The essential consideration here is that you are not giving your son access to your home for Shabbat. Rather, he lives in your home, where his religious observance is apparently better than at other places. Admittedly, your leaving the house does provide him with more comfortable opportunities for chillul Shabbat, but that is not the same as actively giving him a forbidden object or directly “placing a stumbling block.” For example, an attractive woman might cause someone to harbor inappropriate thoughts when he comes in contact with her. However, we certainly do not forbid her from going into the public domain with the allegation that she is “placing a stumbling block” before him. Rather, situations to sin do exist, and one who goes about his life normally and responsibly is not held accountable for the prospect that others will “use” him or his possessions inappropriately.
The circumstances would be very different if non-religious Jewish neighbors asked you for permission to use your house for a party on Shabbat that would include chillul Shabbat. In that case, you would actively and directly be giving people use of something that they did not have before and which is expected to facilitate their sinning. (We do not intend this as a ruling about the latter case. In these matters, various factors and nuances play a major role in determining the halacha.)
The more pertinent issue for you is the obligation of afrushei me’issura, to distance your fellow Jew from sin. This certainly includes your children. The source of this obligation is likely the mitzva of tochacha[4] (rebuke).[5] It is true that we are not accustomed to trying to prevent neighbors from sinning, but that is because we are unlikely to be successful.[6] However, according to your account, your mere presence prevents your son’s aveirot.
The question is to what extent you are expected to act in order to fulfill the mitzva of afrushei me’issura. In general, one is supposed to go to significant lengths to fulfill positive commandments. However, this is to a lesser degree than is required to avoid breaching negative commandments, for which one needs to give up all of his money, if necessary.[7] Are you required to follow your son around all day and give up other activities?! Clearly not! However, it is difficult to present precise guidelines for the efforts that are appropriate under the circumstances. We would thus say that the likelihood of your son’s sinning should be a serious factor in planning your schedule, but you cannot be expected to simply never go away.
Your main goal, in this regard, is to use your relationship with your son to improve matters at their root, as opposed to preventing individual violations. While development of this topic and presentation of its sources[8] are beyond our ability in this forum, realize that it is often more constructive to “overlook” your child’s religious and other shortcomings in order to maintain a positive relationship. While we admire your dedication to every aspect of your son’s religious life, we urge you to be careful that your handling of issues like this does not have a deleterious effect on your relationship and his overall personal/spiritual situation.