The % of both spouses working in married families has dropped from 54.6% in 1984 to 45.4% in 2020. It's possible that the % has increased specifically for families with children under 18 but the main BLS data set only runs goes back to 1994. It's also possible that working women are less likely to get married.
However, the % of working women's contribution to overall family income has increased from 28.4% in 1984 to 37% in 2018, likely as a result of women working more hours, and moving into higher-paying jobs. As a result, single-earner households are at a greater disadvantage now than they were in 1984, despite the lower number of dual-earning couples.