Thank you for your inquiry. From what we gather from the question, you were asking about the risk of HIV transmission in the event that your child had touched a toilet seat with HIV positive fluid.
From the information given, this scenario is determined to be of No Risk (Transmission of HIV is not possible in the given scenario). Although your question is specifically regarding children and their developing immune systems; the scenario you described does not present a threat to HIV transmission.
In order for HIV to transmit, the requirements for HIV transmission need to be fulfilled. According to our HIV Transmission Equationthere needs to be the presence of HIV positive fluid (blood, semen, vaginal fluid, anal fluid, or breastmilk), with direct access to the bloodstream through a High Risk, Low Risk, or Negligible Risk activity.
You are correct in assuming HIV does not survive long outside of the human host. Dry or drying HIV positive fluid undergoes a rapid reduction in concentration, making it extremely difficult to cause transmission (1). For this reason, your daughter is at No Risk for acquiring HIV through public toilet seats.
Recommendation: No need for HIV testing for the scenario provided, please refer to health care provider for additional health related questions.
All the best,
AIDS Vancouver Online/Helpline, Cody