You can see many clothes and shoes markets here:
http://www.guangzhouinformation.com/406/Wholesale_markets/
Most markets are around Guangzhou Railway Station area. You can get there by subway Line 2 at Guangzhou Railway Station. The hotel nearby, I think Liuhua Hotel is good.
There are Liuhua Bus Station, Guangzhou Provincial Bus Station and Guangzhou City Bus Terminal nearby within walking distance. You can find buses there to Zhuhai. You do not need a visa to enter Guangzhou. As to Children theme par, I know Guangzhou Chime-Long Paradise, but it is in Panyu, a bit far from the city center.

I would stay at Guangzhou Intercontinental Service Apartments at the cross junction of Beijing Lu and Tai Kang Lu.
You get the best of both worlds - meaning you have both Orchard Road and Sungei Road (using an analogy of warehouse stuffs) at your door step.

The other hotel you can stay at will be GuangZhou Hotel, just above the HaiZhu Metro. The hotel is located in HaiZhu square (Hai Zhu Guang Zhang, in pinyin)

Behind both hotels, you will have GaoDi Lu (高第路）which is a warehouse street. This street leads you to many other warehouse areas selling shoes, handbags, belts, clothes etc...literally shop till you drop, within hotel walking distance.

You can get to both these hotels after arriving at Bai Yun Airport. Step out from the airport exit doors, you bus queues and taxi queues. Ask around, for Bus Line 5, which will take you directly to Haizhu plaza, in front of GuangZhou hotel in 30-45 mins, with RMB 20/head. (You can get back to airport using the same way).

There's no MRT from Airport. The MRT serves City areas only.

Getting to Zhu Hai, you need to stop at MRT for Guangzhou Railway station. Please do not confuse this with Guangzhou EAST Raliway station (many people does) but they are miles apart, and are different train stations altogether.

At the GZ Railway MRT stop, you will be able to see signs that will lead you to Bus terminal centre. It's just a short 5-10 mins walk. Buy ticket to ZhuHai from there. 2 hrs ride. Easiest is ask ground staff which booth to purchase tickets. All are helpful.

Theme park in XiJiang is fantastic for kids. There's about 10 live pandas there. We loved it. Hire private transport for a day. I have contact - but he speaks only Mandarin.