sexual behavior - 5 years old boy

Hi, sorry for writing in English, I have a problem with my PC. Appreciate if you could answer in Hebrew. My son is 5 years old. When I came to pick him up from his day care (Tzaharon) today, his kindergarten told me that yesterday he asked one of the new boys there (3.5 years old) to come with him to the toilet and touched the private parts of his body. From this reason the little kid was afraid to come to the day care today. I was shocked and talked with my kid about it, while mentioning that we should respect others’ privacy and that it is not acceptable to touch other kids, same as no one can touch him. When I told him that he denied that he did it although I was very calm and didn’t show anger. I have to mention that it is the first time my kid touches someone (at least that I know about it) but there were 3 different incidents in the past when he express sexual interest; The first one was last year when I was told that one boy from his day care asked him to undress to “show” him (the other boy initiated it), the second one was when I saw him showing his organ to one of the girls in his kindergarten and the third one was when my husband found my son and other friend going together to the toilet in our house and didn’t allow them to go together. In all 3 cases we talked with our son the same as we did today. I am very worried. First because it looks like that although we talk with our boy, he continues to be involved in such cases and doesn’t understand the limits, and second because he keeps denying it. What else should I do? Should I update his morning kindergarten about the last case? I know she talks about it with the kids, but should I ask her to keep an eye on him? On one hand I’m afraid that he will continue with this behavior, but on the other hand I wouldn’t want to give him a feeling that he is bad. Should I go with him to professional psychologist at this stage?

שלום רב, את יודעת, השאלות שלך עוררו בי לא מעט מחשבה. כמו שכבר כתבתי כאן פעם, בימים הרחוקים של ילדותנו, משחקים של "רופא וחולה", "אבא ואמא" וכד', היו שכיחים מאד, ואיש לא ראה בהם משהו נורא כ"כ. הסקרנות סביב הגוף ואיבריו המוצנעים תמיד הייתה שם, וילדים מצאו את הדרכים המקוריות לעקוף את האיסור ולהציץ בהם. כיום, הרגישות לנושא רבה מאד, והמשחקים התמימים של פעם קיבלו כותרת חדשה של "התנהגות מינית בלתי ראויה" או אפילו של "הטרדה מינית". רוב הילדים, מצליחים לקבל את ההסבר שנתת, ולהפנים את המסר. עם זאת, יש ילדים שהסקרנות והעניין המיני שלהם גבוהים יותר, וקשה להם לאפק את הדחף, בעיקר כאשר נקרית בדרכם הזדמנות נוחה לכך. אפשרות מדאיגה יותר, היא שהעיסוק המוגבר באיברי המין משקף (חלילה) פגיעה כלשהי שהילד חווה, שעלולה ליצור גריית יתר לא תואמת גיל. אם אפשרות כזו נראית לא רלוונטית במקרה שלכם, כל שעלייך לעשות זה להגביר את הפיקוח ולהדק את הגבולות, ואולי באמת גם ליידע את הגננת, ולבקש ממנה לסייע בהסברה ופיקוח בין כתלי הגן. בברכה ליאת

Thank you Liat for your professional answer. Indeed, I can't stop thinking from the time I was updated by the kindergarten. How would you suggest to start talking with my kid in order to be sure he didn't experience such thing and in a way he'll feel comfortable to tell me? Should I refer to the incident while talking with him or make it totally different conversation?