Ahh got ya. If his child is young probably not a discussion for little ears.
From a lineage perspective, not factually relevant.
From a family history perspective, definitely relevant.
Your marriage to anyone would be important too, especially if you have children together.
Another option could be to include in your own profile or, if you have added your partner, in their profile, a story or summary including your step child/children and their information.
Many blended families with many options these days!