Hi Hayley.....and welcome..
I havent used either of the machines you mention .....but...i would think the biggest question you need to ask the members here who have used them is "will it be light enough for a 10 year old and also will the stem shorten enough for her to use"
So hopefully the guys will be along soon with some advise....
Having said that i would go for the 250 because of the extras and the fact the 250 will pinpoint the targets, which would be a must for your daughter.....
Take a look here at the cscope 3mx which has been reviewed with a video by one of our members....it is slightly more expensive but might prove lighter......and it is a good machine
http://www.metaldetectingforum.co.uk/vi ... =25&t=2746
Here is another piece written by one of our members concerning the Cscope 3mx
Went to a little shop in Dewsbury and got me c scope cs3mx.The chap in the shop is a detectorist himself and gave me lots of good advice . I cant get over how light it is and it really is so easy to use. thanks again everyone for the advice. cant wait to go on my first outing now.Lynn