I don't have any tips, just know you are not alone. DS used to go to bed anytime around 6 or 6:30 but now he fights sleep even though he is tired at bedtime. Lately he's been going down anytime around 7 or 7:30 (closer to 7:30) but there were a few nights where it was anywhere between 8:30 and 9:30. I have had to resort to CIO, which I hate but I only let him cry for 5 minutes before I go in. Sometimes he goes to sleep before the 5 minutes is up, other times I have to go in there after 5 minutes, lay him back down (because he stands up and screams/cries) and then rub his back or belly until he settles down. I think they are honestly just at an age where they are learning so much that even though they are tired they don't want to miss anything by going to sleep.
