Beijing can be a great place to visit with young children provided that you exercise the normal awareness you would at home and also make suitable preparation for your days out. There are many places worth visiting and both entrance fees and public transport fees are usually waived for kids under 120cm (not applicable for domestic air travel). Concessions may apply for children between 120-150cm. The following website may give you some ideas as to what's on offer:

Children are treated incredibly well in China, particularly Western children.  Blonde and blue - eyed and you may feel like the parent of a minor celebrity. It is probably easier to cope with for older children (say over 7) but young children and toddlers may find all the attention a little overwhelming - be prepared to say no to cuddles and photos if you feel you need to. Bear in mind that Beijing is a densely populated and super-busy city with serious traffic congestion and more than its fair share of poor drivers. Be especially careful near or crossing roads and also in large crowds. Remember that pushing and shoving, cutting in line etc. does not carry the same social and cultural stigma as may be the case in your home country.

Beijing is a big place and its attractions are spread out and often cover a large area themselves. Don't leave your stroller or fold-up pushchair behind if you normally use one. Taking a taxi is probably the wisest choice for local travel as both the subway and the buses can get incredibly cramped, especially during rush hours. You can also look into hiring a car and driver if you have more people than will comfortably fit in a taxi. Allow yourself extra time and don't skimp on how long you stay in Beijing so that you and your kids can get to see all you want.

The recommended section of the Great Wall to visit with young kids is Mutianyu. The traveling time from downtown Beijing to Mutianyu is 1 hour 20 mins by car in good traffic condition.  You can take a cable car up, turn right and walk (mostly downwards) for an hour or so until you reach the slideway, or toboggan, to return to the bottom. There are double-sleds for parent and young child. Older children are permitted to slide by themselves. There is also a chairlift down or just the steps. Mutianyu is a restored section and caters well for tourists. It is not as difficult to negotiate as any other section but there are still some big steep steps where toddlers would need to be carried. This is one place where you should leave the stroller in the car. 

With a little planning and preparation, you and your kids can have a great time in Beijing. For a look at three "ideal" itineraries for Beijing with kids, check here. Former Beijing locals have created trip lists for babies, kids and teens. Additional information may be found here: china-family-adventure... but please note that, contrary to some statements here, if you try to fly a kite in Tiananmen Square you'll soon end up being reprimanded by the security forces.