Hey, I know what you're going through. I also suffer from POCD, and it peaked when I was about your age. I remember being on a boat tour with some 11 year old girl, and my mind wouldn't stop trying to convince me I was sexually attracted to her. This was before I even know I had OCD, but I knew that something was wrong with me and wanted to see a therapist.
Are you currently seeing anyone for your OCD? If not, then of course I'd highly recommend you do so. But for now, as someone who's gained control over multiple types of OCD (POCD included), the best advice I can give you is this: the less you resist your intrusive thoughts, the less powerful they become. Like any other form of OCD, refraining from doing the compulsion is the best thing you can do to minimize the obsessions and anxiety. In the case of an obsession that has no physical compulsion like POCD, the compulsion, then, becomes the act of resisting the thought itself. Perhaps you may try to think about something else, or you repeat words in your head to distract yourself. Anything you do that is meant to keep you from thinking about the intrusive thought is a compulsion that you eventually have to stop doing. Let the intrusive thought live in your head, even though it may give you anxiety, and eventually it will go away on its own. The more you do this, the fewer intrusive thoughts you'll have, and the ones you have will be less anxiety-inducing.
Avoiding the 3 year old and any other child will give you temporary relief, but in the long term it won't help your intrusive thoughts. I'd recommend seeing a child just for a little bit, while practicing what I wrote above. If it works and you feel a little better about seeing the child, next time see him/her for a bit longer. The goal is to make each visit slightly challenging, but not too challenging.
I'd highly recommend meditation for something like POCD. The idea behind meditation is to watch your thoughts and separate yourself from them, so practicing these things will help with dealing with your intrusive thoughts.