I am steadilly putting a childrens act together and did a gig with it on Sunday.
I don't have any big illusions, can't afford them but I kept quite a diverse age group happy, and laughing with the following programme.
1) Production of an 8' drinking straw from a small lunch bag. This is a great gag, very visual, relatively cheap and very easy. I dress it up with a story about having my lunch first and have a squeaky hot dog as part of the gag.
2) TT silk vanish. I took the routine out of the Seriously Silly book by David Kay, I will talk about this later.
3) Basic spongeball routine. The kids just love to guess how many balls you have in your hand and will shout like mad.
4) I have a glove puppet parrot called Archie. I bought him for £15 from Mike Danatas Magic Studio. He has a squeaker so I can make him say anything I like by interpretting for the children what he says. I play him a bit like Emu, a bit naughty but get him to help with a trick called Metamorpho Spots. This is plain handkerchiefs to spotted in a can. I then have a bit of a struggle getting him back in to his bag which gets a good laugh.
5) Appearing bouquet from a vase. My single most expensive piece of equipment, again from Mike Danata, £35
6) Rabbit from a hat. Not a real hat or rabbit, its a two silk trick with a TT. I then segue this in to putting the produced rabbit silk in to a change bag and bringing out a toy rabbit.
7) Cups and balls basic routine with a chop cup finish. This was a disaster. My super ending got screwed up because my wife who was helping me moved the balls after I had started and the chop cup ball got put in out of sequence and didn't stay in the cup when I needed it to!!

My finale was a three part Magic Colouring book routine. I tried out the Seriously Silly one this week but didn't like it so will go back to the one I usually use
I also have a magic egg can and would usually make this my finale but some of the kids at the party had seen me do it fairly recently and it rfelies on its end for the main effect.
I referred to the Seriously Silly book by David Kay. I bought this a couple of months aga and have mixed feelings about it.
The good side of it is that it does have some good advice about audience managment and about how to split children by age groups and how to treat the different age groups.
The down side is that it repeats itself a bit, it looks like he has written a series of shorter books or articles, strung them all together and edited them badly. He also advocates using some tasteless stuff to get a laugh. I just couldn't and wouldn't do it and don't see the need. Kids will laugh faitly easilly at quite harlemss stuff. I also got a bit fed up with his name dropping and self adualtion.
Any way, I hope that this helps. If I added up how much my act had cost to put together I suppose it would not come to much over £150.
As you will find in here there is a truth which runs through all types of magic - from putting out a couple of tricks for kids to Derren Brown and that is
"It isn't the trick its the performance"
As true for a 5 year olds birthday party as it is for any adult show.