I've tried different antivirus like Avast, AVG, Avira, Kaspersky but until now the best of them is ESET.
Among them, ESET has the lowest memory consumption. So it should run smoothly with low-end devices.
It also scans your files automatically and has a good web monitor, prevents you from visiting untrusted sites and also detects if someone has a duplicate IP within your network.
Even you won't bother letting a kid use your PC because you know it's safe.
I'm just sharing my experience as a tech support.