Thankfully mine are old enough to tell us when they're not feeling well and having a headache

They look unwell and may indicate on temples or area that hurts

He will have a pained look which I know is headache

Their body language and constantly crying perhaps

Not very sure. Its usually my kids will tell me

How do you tell if they didn't tell you?

She will always tell me her head hurts

If they have Low energy I always checj

If they’re complaining of one 😂

From their expression and behaviour