Seriously - they will be dropped, kicked, tossed in water, mud and lord all knows what else and eventually end up broken or lost. Nothing against your kid......it's just kids in general.....I have 4 of my own.....they could lose and break a 100 lb anvil! Spending good money on top end optics for kids is not a good idea. Go to wal-mart or the like and buy some cheap Tasco or the like.
On a serious note something low cost but with as high magnification as you can find and with a wide field of view. Kids have a hard time finding what they are looking for and the closer they feel to the critter the more they will use them. If they can scan with the wider view and then "zoom in" they will get a kick out of that. Good luck.