And I mean it in that order. And this goes double for step or blended families. In nontraditional families parents tend to lean in the direction of their biological children. Acknowledge that pull as healthy but don't let it pull you apart from your partner. That is not healthy.
Children are concrete thinkers.
They need to see, hear, feel your commitment. Write it on a certificate and stick it on the refrigerator door along with the grocery list and the daily artwork. Talk about it at the dinner table. Show it in your willingness to show up at their school play or go on the bus for the school field trip. This can be hard for children of divorce or abusive homes to trust.