What state do you live in? If it's a state that still doesn't permit adults adoptees to get a copy of their original birth certificate, I encourage you to write to the governor and legislature of the state to support this. We need adoptive parents to support our quest for adoptees' rights! If you need help in figuring out who to write to, let me know.
Part of who we are today is written in the past.
Your children are fortunate that they found their birth families at a young age. I met my siblings for the first time at age 60.