One way to plant gospel seeds in the conversations you have with your kids is to explain to them why you do what you do. Listen to Kurt Gebhards:
When a parent makes important decisions in life, he should explain to his children how the gospel influenced that decision…explain why you do not buy certain things, do certain things, and constantly point back to the gospel as the motivation (taken from Evangelism: How to Share the Gospel Faithfully).
Now, in order for this to be genuine, you must actually make decisions because you have been influenced by the gospel. So, I think the point is that planting gospel seeds in conversation with your kids will not be difficult if, in fact, you are living a life that is focused on the gospel. Gospel conversations will take place simply because you are answering the question, “Why?”