There are many places selling children's clothing, including shopping malls on the pedestrian streets, but they are all relatively expensive. I recommend you to go shopping on Xinhua West Street near the exhibition hall. There are many stores selling children's clothing there with many styles. Prices can also be negotiated, so you can go take a look.
In addition, there are many Tongxin Road markets in Xixia District, which are generally cheaper, but the quality cannot be guaranteed. If you are not far away and don’t mind the trouble, you can also go and have a look!