The labour dispute spread into the western state of Rhineland-Palatinate, where public workers' union said some 2,000 to 3,000 day care and social workers would walk off their jobs at some 100 childcare facilities.
Meanwhile in Bavaria, workers from children's services and state-run social work offices also joined the strike after some 400 day care centres closed their doors on Monday.
Kitas in the states of Hesse, Baden-Württemberg, North Rhine-Westphalia, Lower Saxony and Saarland remained closed for the third day in a row.
More than 2,000 childcare providers are expected at a demonstration held by Verdi and the Education and Science Workers' Union (GEW) in Frankfurt.
On Monday, some 15,000 workers participated in the strike, while 11,000 took part last Friday.
The strike has forced parents to scramble for alternative arrangements or stay home with their little ones.
The unions have said then they were prepared to dig in for a long-term battle.
Current wages for 220,000 educators across the country are unfair, and workers need better healthcare options to handle the strain of their jobs, they say.
The next round of negotiations with state employers is planned for May 27.