(a) Age of the children is an important factor to decide the product. Whether it is for daily use or for occasional use, is another factor.
(b) The features available in the wrist-watch is required to be decided in advance. Personally I prefer minimum features.
(c) The cost is, needless to say, is important. The children should not be costly items. This is necessary for their safety and security also.
(d) The colour, band, style, dial, etc. can be decided consulting the children.
(e) Various categories and types of wrist-watches and their basic features can be checked and compared at various e-Commerce sites like Amazon, Flipkart, Myntra, Jabong, etc.
Beware! I question everything and everybody.