For the last several years I have tried to avoid mailing paper checks. Not only do I worry about the check being stolen & washed (I have purchsed gel pens on Amazon for check writing) but many times my mail just wasn't being delivered.
It doesn't matter if it's a "safe" area. I live in a very safe area but still bring something like this to the post office
Here is one example....my daughter got married in May of 2022. We mailed out invites almost two months in advance.
At one point my brother asked when will we mail the invitations. He was living in St. Louis and we are in PA. I told him that it had been a month already but he had never received it. So DD mailed a new one. Both arrived together two weeks later. This was not during the holiday season when you can imagine mail being backed up! I've had other examples of mail either not arriving or being very late.
If I had to send funds I would try to see if you could send it via Venmo or an app like that. It's very easy to use but your son has to have the app too. Once you set it up you can see how easy it is to use and there are no worries if the check will arrive. It works instantly.
Or you could go to the post office and have the check mailed either Priority mail or registered mail. You would have tracking for the check where you just wouldn't by mailing it with stamp.