Simple or Complex Trust

My kids have an irrevocable trust in their name created to deposit gifts from my parents through the years. I am the trustee until they reach a specified age so that they are not taken advantage until they are mature enough to make mature decisions. I am the Trustee. The funds are in investments, CD's and Savings Accounts and the earnings are theirs and automatically reinvested in the same accounts. For filing taxes on these earnings, is this considered a Simple or Complex trust?