Please can anybody help me.

I want to make a figure similar to this one -  http://cakecentral.com/gallery/2314602/cleaning-lady.

I am making a cake for my grandsons birthday and I want to make a figure of him standing but dont know how to do it without it falling over

You could use some sort of dowelling to connect the figure to the cake (a toothpick might not be strong enough, but you could use something like that). Add the dowel to the figure while making it so that it sets into it before attaching it to the cake.
Depending on how wide the base is, if the weight of the figure is even for it to stand on its own, you coul "glue" the figures to the top of the cake using chocolate.

Skewer the legs. Make the legs around wooden skewers, leaving at least 3" of skewer on each side of the legs. Let the legs dry as you work on the body. Slide the upper exposed skewers into the completed body and the lower exposed skewers into polysterene and let the figure dry. When you're ready just stick the skewers into your cake wherever you want it.

This might be a better example - http://cakecentral.com/gallery/2312084/blues-clues