Completely normal for that age. You can't do it to anyone else - but for your own child there is this nasty tasting clear nail polish you can buy which is supposed to stop thumb sucking. I used it on my son when he was constantly eating his boogers and it worked within one week. (I only put it on the finger I knew he used to pick his nose. It is really really awful tasting and it can get on their food and ruin the taste)
