From experience, I find that Children are the most difficult audience to entertain and my performance is definately geared towards adults. I've tried a few with the spoinge balls etc. and it just didn;t work for me so I have the greatest respect for those who can, and do perform for children.
There are points that I agree with and disagree with that havw already been written here. I would say that the experienced children's magician will be able to judge the audience and go with the flow. Some will appreciate the BAM BAM BAM type effects (hard work by the sheer number of tricks) whilst some will appreciate the slow half dozen tricks spred across an hour or so. It is about being entertained but the perception of the show may well be different for both the children and the adult(s) who are paying and watching.
Whatever your style, I think that you need to talk through your performance at the time of the booking so that the person making the booking knows roughly what they are getting. If they are expecting 40 tricks and you give them just six then it is partly your fault for not setting out your stall properly. Likewise, if someone queries why they are getting just 6 tricks then it's your job to convince them.
One thing, and from a non children entertainer - I would suggest that one of the critical factors for entertaining children is the audience participation bit

Member of the Magic Circle & The 2009 British Isles Close-Up Magician of the Year
It's not really an optical illusion - it just looks like one!