Investopedia discusses how to set up a trust fund if you're not rich:

Trust funds are designed to allow a person's money to continue to be used in specific ways after they pass away, and to avoid their estate going through probate court (a time-consuming and expensive legal process). But trusts aren't only useful for ultra-high-net-worth individuals, the middle-class can use trust funds as well, where setting one up isn't out of financial reach.