I know nothing about Ohio law but since most divorce laws are the same, I’ll take a shot. First, DOCUMENT everything (I always say this but it is critical.) Document the time you spend with your kids, the time SHE spends, when she drops them off, when she calls – everything.
Next, take your kids to see a therapist. Since they are young, take them to see one who specializes in children’s art therapy. Kids the age of yours love to draw and usually use it as an emotional outlet. You meet with the therapist first and tell him your fears and then let him/her do what she can to draw out whatever may be true for the kids. No only will you get some good evidence but you will also position yourself as a concerned dad (always helpful).
A father getting young daughters is VERY HARD. But the courts seem to be waking up. Just gather all the evidence you can. Remember, anti-family court is still a court which means the rules of evidence still apply. The only things that count are things you can prove.