Portable DVD players have become the thing of today and many people already own at least one.  Here are a few things to consider when deciding what to buy. 

Most portable DVD players offer AV out capability meaning that with the proper AV cable you can hook it up to any TV with AV ports and even older TV's with the help of a RF converter.  If you are considering purchasing a DVD player for your child's room, consider a portable DVD player since it will serve that purpose and also adds the additional convenience of taking it "along" on a long car trip and/or a plane ride... even any other room in the house, to a relative's house, babysitters.. the possibilities are endless.  Having one of these at your disposal can be a godsend and can entertain your child for hours when they might otherwise tend to become impatient and antsy.

There are many different style portable DVD players out nowadays and your choice may just well depend on your preference.  Here are just a few pointers..

Tablet style - These are the newest flavor and therefore tend to be a little more pricey; however, they are very easy to mount to the back of a car's headrest without much fuss and are far more secure than the book style players that mount to the back of a car via straps and are less secure and more cumbersome.  However, one thing to consider with this type of player is that the screen is always exposed because it doesnt have the benefit of a closeable cover and is therefore more prone to scratches.  It is especially important to transport this type with a padded bag or case so as to protect the delicate screen as much as possible.

Book style with swivel screen - These handy models combine the convenience of a headrest mount with the ease of standing on it's own on a table or other flat surface for watching without having to hold the player (which can become heavy while watching a 2 hour movie).  Some tablet players have some sort of stand that allows you to set it on a table for watching, however, it does not allow you to change the angle of the screen to that which the person viewing feels most comfortable with which this type, like the traditional book style ones does allow.  Beware; however, that even though the swivel mechanism may be handy, they tend to be delicate in that they will not take much abuse and could break if handled roughly.

Traditional Book style - These are most common and have been out the longest and they have the added protection of a cover for the screen when they are in the closed position.  This is especially important when they are going to be handled by children.

These are the 3 main styles of portable DVD players on the market; however, you will also find many different varieties of what people will call "portable" DVD players that are not really entirely "portable" in every way. 

Important things to check for:

Does the player have a built in screen?  Some so-called portable players are without screen's and are only called portable because they are smaller and can be moved around with greater ease; however, unless you have a separate monitor or TV to hook it up to you would not be using it "on the go".  

What is the screen shape/size?  These can range from 3.5" to 10" and even 12" screens and are available in the traditional 4x5 and the widescreen format (which is wider than it is tall - the way most movies are made nowadays).  Depending on how "portable" you want it.. a 7" screen size is a happy medium, allowing a large enough screen area to view comfortabley from a few feet away (such as from a car headrest).  The larger the screen the higher the price and the less "portable" and more bulk it is to carry. A tiny screen such as the 3.5" ones would be a nice "take everywhere" portable that a parent could throw in their purse or child's backpack and take essentially anywere you might think the child could possibly use it (yes, even in a doctor's office waiting room).  The screen size is fine for one child, but it would be hard for two to watch comfortably as the child would want to hold it closer to them to be able to view it more comfortably. 

Rechargable battery - Beware some car systems do not have this option yet it is critical if you want to take the player on an airplane or elsewhere where a power plug may not be available.  An alternative would be an external battery which is available but would be separate from the player therefore adding another accessory for you to carry along. 

Car Adapter - Allows for the option of using your vehicles cigarette lighter for power.

AV connections available (and proper cables) - Some have only AV out, others have both in and out.. the in allows you to hook up a gaming system to it so that you can view it on the screen instead of a movie, a handy alternative for bigger children.  The out allows you to play the dvd and project it onto an external screen, such as a TV (can be handy when traveling if your hotel room doesnt have a DVD player). Most manufacturers include the necessary cables you will need to accomplish this. 

These are just a few things to consider when purchasing a portable DVD player.  I have owned quite a few of these and from my experience I have found the following:

-  the tablet style are handier for use in the car

-  the 7" screens are large enough yet not too bulky

- even if it comes with a rechargable battery, an external one is nice and adds an extra few hours of enjoyment when AC power is not available

I have owned a few different brands and really would just recommend that you try buying a well known brand (do your homework and find out what the ratings are for the brand and/or model you are considering - this can help alot in making up your mind)

I am not an expert but I do hope this helped make your decision a little more informative.