Hi Bluetreetop,
You might want to try looking here for a good selection of Xyron products and their refill costs.
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Since you are talking about a 4 year old, I would suggest that you think carefully before you buy. Although the machines are all relatively inexpensive, consumables are your biggest costs in the long term. It might also be worth considering a Xyron that could be used around the home if it falls out of favour with your little one. The Create-A-Sticker X150 will only make narrow stickers (2-3cm width) and is a pull through process with a plastic serrated edge to cut off the resultant sticker. Nothing on it to hurt little fingers really...but still would need supervised by mum or dad. Positioning the stickers correctly and close together may not be so easy for small fingers and result in loads of waste from the adhesive roll. I am not sure that a 4 year old would have the manual dexterity to use this effectively, as it sort of requires sliding in and pulling through simultaniously. I have a Xyron 250 which works by turning a handle and allows for slightly larger stickers (5cm or so wide). Similar to the above, still requires careful placement to avoid too much waste. Seems to be popular for childrens playgroups etc.. as it is not too big and has nothing sharp. Again, it has a plastic serrated cutting edge. Looking here I see that there is suggested age limits for certain kits:
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Check them out also :o) There is a Xyron 510, which makes stickers, labels, laminates and makes magnetic stickers. This machine is more versatile, but I believe it has a tiny blade (same as the 900) to cut off the resultant item. If you consider that each of the cartridges will run at about £10 each...you can soon clock up a fair amount of money. This machine has 6 different types of refill available.
Then there is the 900 or creative station, which will do all the tasks the
510 does but up to A4 in width. I have this one that I use for photos and photomats.
Basically, they all work on the same principal by placing item face up, pull through or turn handle. When it comes through other end it is covered with a clear film with the adhesive strip attached to the back of the item. All you need to do is remove the clear film, similar to cellophane and peel off your stickers.
HTH