A joint return is one tax return that lists your combined incomes, deductions, credits and dependents. Yes, you list your child dependents on your joint return. If these are step-children of one of you, you can still list them since step parents have the same ability to claim a child dependent as a biological parent.
Children are your dependents if they live with you more than half the year and meet a series of other tests that Turbotax will ask about.
The only reason you might not is if there is shared custody with another parent (someone's "ex"). The interview will ask about this too.
