Guinea pigs rarely bite but it is quite easy to drop them by mistake. If they are dropped, they may break a limb. So children need to learn how to handle guinea pigs and to remember that they must be securely held, never grabbed, and never squeezed too hard. All children should be supervised at all times. Always use both hands.
Slide one hand under the guinea pig’s chest, putting the thumb over its shoulder. With the other hand support its backside and its weight. There is a nice video here. After picking up a guinea pig, then hold it against your body so that it feels secure (Kaiser et al., 2010). If you are going to stroke your guinea pig, do this at ground level, with it sitting on your lap. Guinea pigs live on the ground so being held high up may make them anxious. Occasionally a guinea pig which has had enough stroking will give a little nip to tell you so (McBride 2011).
If you have a guinea pig which is very frightened or difficult to handle, you could think about training it to go into a small cat carrier by putting treats in the carrier. That way you can take it to the vet without having to chase it round the cage or hutch. Read Can I train my guinea pigs to do tricks?
Kaiser, S., Kruger, C. & Sachser, N, (2010), ‘The Guinea Pig,’ in eds Hubrecht & Kirkwood, J., The UFAW Handbook on Care and Management of Laboratory and other Research Animals, Eight Edition, Wiley-Blackwell, Chichester, UK, 381-398
McBride, A., (2011), Guinea Pigs. Understanding and caring for your pet, Magnet & Steel.