IKEA extendable children's or adult bed frame (mattress not included). The bed ends can slide toward each other reducing the overall length. Full size 80x200. Good condition. It's an IKEA Sundvik bed. https://www.ikea.com/gb/en/p/sundvik-ext-bed-frame-with-slatted-bed-base-wh...
You can get special extendable mattresses from IKEA to grow with you child, or just put a full size mattress on it.