Know what you want
When entering into a relationship, you should have a set of values you are looking for.
If it’s marriage or children you are after, you should know what those mean to you as this will assist you to choose a partner.
You can have a conversation with your partner about those values to see how he thinks about them.
Alternatively, observe the way he behaves around people.
Take notice of how he treats children and his siblings to get a good sense of how he feels about family.