The grocer has sold John Lewis-branded babywear since 2003, but is trialling a clothing range for children up to eight years old in its Canary Wharf store. If successful, the initiative is likely to be extended to more stores.
Waitrose is also considering increasing its store portfolio. It currently has about 180 outlets, but marketing director Christian Cull said the grocer was hoping to boost numbers by 40%.
The chain, which is largely based in the South, has recently opened stores in the North and Scotland.