Try consulting an ADULT psychologist for advice. By their age, the kids know you're dad. No matter how many other dad-substitutes, mom's boyfriends, or step-dads may cross their paths in life. You are, and always will be "dad" to their hearts and minds. If you're having feelings of uneasyness, inadequacy or of fear being replaced, which are all very common to dad's in your situation, keep in mind that those are YOUR issues. Get help for the issues YOU are having before you TURN THEM into an issues for your children. Trying to get your children treated or evaluated for issues they don't HAVE, only opens the door for CAUSING issues where none existed - starting by making the children wonder why you think something is wrong with THEM.