If its clear that the person is very undecided about what to purchase and is basically asking for help then I will steer them in the right direction. However sometimes it will backfire on you because they won't understand to buy the 50$ game over the 30$ game, then you have wasted your time.
Sometimes to make a happy child you have to buy whats on the list no matter what, as they won't accept items for gifts that are not from their list. If it makes a kid happy then you HAVE to buy whats on the list no matter what, and believe me I know this from experience. Sometimes making a kid happy has to override what you think is a good game.
Another thing is that children almost NEVER know what they want, they can spend 2 hours in a game store browsing and still be undecided. They are just too young to have actual tastes in gaming and to know which games are good and which are bad, unless you have older kids who are really in the know. Most kids however will tell you they just buy whatever looks good on the shelf. They also seem to actually play and enjoy games that are considered bad by the general public, which is a scary thought.
The Gamestop employees here are actually pretty honest with undecided buyers and they will try to steer them in the right direction usually. They almost always steer potential buyers for Wii games towards Nintendo's first party titles. This creates more sales for them because if they made a suggestion that someone buy Action Girlz Racing for the Wii for their little girl for X-mas, I don't think they would get very many customers coming back to them. FYI Action Girls Racing got a 0.8 on IGN as a review score, the lowest review score I have personally ever seen for a console video game. I know Gamestop employees don't have logic most of the time but the ones around here seem fairly honest.