Occasional lapses in memory is a normal part of aging such as forgetting where you put your car keys, forgetting where your eyeglasses are etc.
That's a normal part of aging and even younger people sometimes forget things as do I sometimes which is normal and not part of dementia.
Forgetting who people are and especially who you're kids are etc are signs of dementia but just normal forgetfulness it usually not a sign of dementia as long as it's just occasional.