Traditional platforms like eBay and Gumtree are still great options for buying second-hand clothing, furniture, toys and electricals. https://www.ebay.co.uk/ https://www.gumtree.com/
Vinted and Facebook marketplace can be great options for clothing, toys, gifts, and books. You can also sell items to earn extra money, or fund new necessary purchases. https://www.vinted.co.uk/ https://www.facebook.com/marketplace/