If you are the parent of a minor child, there are two crucial decisions which you should make and incorporate into your estate plan in order to protect your child. The first involves who will raise your child if you die and the second is who will be in charge of the assets or money you leave to provide for your child after your death.
When the parent of a minor child dies (assuming that there is no other parent living or available), a guardian must be appointed to raise and care for the child. This is the person who is responsible for the day-to-day parenting of your child. In your estate planning documents--and particularly in your Last Will & Testament--you should designate who you want to be your child's guardian. If you do not make this designation, then a court and/or a governmental agency will decide for you.
In addition, you should designate who will act as trustee for the assets which you leave to provide for your child. This is the person who will invest, manage and pay out the monies available to meet the child's needs for items such as health, education, maintenance and support.
So can the guardian and the trustee be the same person? Legally speaking, the answer is "yes." The question is whether you have the right person to serve in both capacities. In some cases, you may have a great person to raise your child but they may not be the ideal person to manage the money. In that case, you might name one person as the guardian and someone else as the trustee. If you have a person well-suited for both positions, then so much the better. However, if you name different persons to the two positions, you should consider whether these two people will be able to work together for the child's best interests.
Finally, as an estate planning attorney, I recommend that parents of minor children name at least a primary and one alternate when it comes to the guardian and the trustee. That way, if one cannot serve, then you have named a back-up person to step in. Of course, you're notlimited to naming a primary and one alternate--you can name as many persons as you have available.