Is there a way to make a text or object of a slide master be on top level of a child item?

Use the footer to put text on the slide master and layouts. The master footer will sit on the slide; if you send the slide's other content to back, the footer text will sit above it.

You can insert an image on a master slide that is shown in front of everything else by inserting it as an ActiveX image control.

1. If you are using PowerPoint 2010 or later, show the Developer ribbon group by going to File>Options>Customize Ribbon, and selecting Developer in the right-hand list.
2. Open the Slide Master view.
3. From the Developer ribbon tab, Controls group (or equivalent with older versions of PowerPoint), click on the Image control (looks like a mountain with the sun above it) and click on the slide to insert it.
4. Right-click on the inserted image control and choose Properties to obtain its Properties dialog.
5. Click on the … button on the Picture line and select the picture you want to show.
6. Optionally, modify PictureSizeMode to fmPictureSizeModeZoon so that the loaded image resizes to fit the control.
7. Optionally, modify BorderStyle to remove the border, and BackStyle to make any part of the control not covered by the picture transparent.
8. Drag the image control to the size and position that you want.

For text, you could do a similar thing using a label control instead of the image control.

You can also just insert a placeholder for text or image (or any other placeholder) on the slidemaster, and then fill-in the placeholder on the master. The placeholder can be positioned on top of the placeholders for slide contents.

1. View Slidemaster and edit top slidemaster or a sub-slidemaster layout

2. Insert Placeholder (Slidemaster Tab, command Insert Placeholder). Choose Text or Image

3. Place the placeholder in front or in back or in between other objects on the layout as you wish.
4. Insert a picture in a picture placeholder: While in View Slidemaster mode, select the placeholder, use Home tab, Shape Fill, and choose a picture.
5. Insert a text in a text placeholder: While in View Slidemaster mode, just edit and format the text.