I am a great believer in teaching children the safe use of knives as tools. This is best done with one on one supervision in the home, starting with food preparation. Our children started before the age of 3 helping make a fruit salad using a blunt table knife to cut up banana. Even though the knife was blunt we would teach them how to hold it safely and effectively. Once they were very comfortable with this they could use a sharp knife again supervised for cutting up say cucumber. By age 5 they were comfortable with sharp kitchen knives and a good help in the kitchen.
This was about the time we introduced whittling knives, they had already proven they could use knives responsibly as useful tools.
When our children were aged 6 and 9 we were staying at the National folk craft school at Sateglantan in Sweden and visited the knifemaking town of Mora and had a guided tour of the Frosts knife factory. Mora knives are world famous as high quality but good value woodcarving knives. We went round the factory with the owners and with Wille Sundqvist a woodcarving teacher who has been a great inspiration to me. At the end of the tour the owners turned to the children and said "would you like a knife of your own?" and gave them one knife each. One of these.
Shortly afterwards Wille gave the children lessons in carving the famous Darlana horses
So what makes a good childs whittling knife? I like fixed bladed knives for proper woodcarving and the little frost knife above is good although the blade guard can get in the way and is not needed. This frosts classic mora knife is also excellent and has small handle suitable for children.
balder made in Norway. This has the benefit of a nice leather sheath and a stainless steel blade that won't rust if put away wet.
All of these are excellent little knives and vary between £10 and £20. Now some people recomend a round tipped knife as a first knife and this one is popular.
Whilst the point at the tip is responsible for more than it's fair share of cuts I find this degree or rounding unnecessary and it makes a knife which any child can see is not a proper knife. Instead I would recommend simply taking some coarse emery paper or a rough old carborundum stone and just blunting the tip a little.
Finally I would not rule out a folding knife, our children both love their Swiss army knives and it is very hard to beat.
I would also recommend "the little book of whittling"
This is not serious adult style woodcarving but is full of great inspirational and achievable little projects for children of all ages.
As with adults carving with knives safe technique is of the utmost importance. Teaching the correct way to hold a knife, always thinking if the knife slips through what I am cutting faster than I expect where is it going to travel? Does it stop safely due to the correct body stance or does it swing out of control into a leg or another person? Our children always enjoyed taking a frech hazel or willor stick and whittling it into a walking stick, magic staff or spear. Hope this is helpful. Happy carving.