Children's shoe listings need a foot-length check because kids grow quickly and brands vary.
Quick answer: CN 29 is about US 12C and 18.0 cm foot length. CN 34 is about US 3Y and 21.5 cm foot length.
If the listing shows CN 29, compare it with about 18.0 cm foot length before ordering.
CN 34 is usually near US 3Y, but measure the child's foot first.
Kids shoe size labels vary by brand.
Leave a little toe room, but avoid shoes that slide.
This page answers one specific size search intent. For the best fit, start with the linked main converter and use the centimeter measurements on the Chinese chart whenever they are available.
Marketplace labels are useful shortcuts, but brand charts, garment type, fabric stretch and body measurements can change the final fit. Treat the lookup as a nearest match, not a guaranteed size.
Chinese size labels are practical lookup shortcuts, not universal brand guarantees. A CN shoe label, clothing size, bra code or Taobao chart row can vary by seller, product category, last shape, fabric stretch and whether the chart shows body measurements or garment measurements.
When possible, use the centimeter value first: foot length for shoes, bust/waist/hip for clothing, under-bust and cup difference for bras, and the specific Taobao chart row for marketplace listings. Then use the converter result as the nearest US, UK or EU match.
For the broader explanation, read Chinese shoe size chart to US complete guide. For why these pages give estimates instead of promises, read Chinese shoe sizes and foot length.