Four children’s retailers have signed leases at Assembly Row in Somerville.

Stride Rite, Gymboree, Carter’s and OshKosh B’gosh outlets will open starting in August, developer Federal Realty Investment Trust announced. A new children’s play area will open Saturday at the Baxter Riverfront Park.

The first stores opened in May at the $1.5 billion mixed-use development on a 45-acre site along the Mystic River. The first phase includes 300,000 square feet of outlet stores, restaurants and the AMC Assembly Row 12 theater, 100,000 square feet of office space and 450 apartments.