At the front door in the morning, tea goes into a small water bottle. Once barley-tea season is over, it is tempting to pour in the hojicha the household already has. The roasted brown liquid looks gentle enough. Yet it is a tea brewed from tea leaves.

Before the lid goes on, the hand pauses for a moment.

No line drawn by age

A child's health handbook lays out its markings month by month with care. For when a child may start on hojicha, there is no such marking.

The national weaning guide says that before weaning begins, breast milk or formula is a baby's best source of nutrition. What it sets out month by month is how meals progress, not when tea begins. Overseas bodies, too, give their guidance as ceilings per kilogram of body weight or per age band.

The handbook's markings, traced with a finger, have nothing more to say here. What can be used instead is the measure of body weight.

Reading the bathroom scale

After the bath, a child peers at the number on the scale. The lighter the child, the smaller the guidance.

The European body gives children and adolescents a daily figure per kilogram of body weight. Japan's national sleep guide notes reports of effects on sleep even below that amount. The Canadian body sets a daily amount for each age band.

The guide adds that children are affected by smaller amounts than adults, so care is needed. The amount in one cup comes next.

How much in a small teacup

From the back of the cupboard comes a child's small teacup. The amount in one cup is the strength of the tea times the volume of the cup.

Brewed the way Japan's food tables set out, hojicha comes to the same strength as sencha. Set the daily figure worked out from body weight beside the amount in one cup, and the number of cups follows. A worked example is gathered at the end of this piece.

For the little cup, too, the only measured figure is for a cup brewed under set conditions. Caffeine across drinks is gathered in the overview Hojicha caffeine: when, and for whom?.

The water bottle, and other drinks

On a park bench, a child twists the lid of the water bottle. The daily guidance takes in drinks other than hojicha too.

Japan's national sleep guide notes that children take in caffeine not only from tea and coffee but also from drinks such as cola. Chocolate contains caffeine as well. The same guide gives barley tea, made without tea leaves, as an example of a swap.

For a child with a particular constitution or a medical condition, the family paediatrician is the one to ask. The sources go no further than the guidance figures. The difference from barley tea is also covered in Mugicha, sobacha and genmaicha. The figures and sources follow below.

The numbers in detail

Weaning guide
“Guide to Support Breastfeeding and Weaning” (March 2019), posted by the Children and Families Agency. It names milk as the best source of nutrition before weaning begins, and finds no nutritional value in giving fruit juice or ion drinks before then. It says nothing about tea or caffeine.
EFSA
Its 2015 opinion proposes 3 mg per kg of body weight a day for children and adolescents. The Austrian Agency for Health and Food Safety (2017) regards this amount as safe for ages 3–10 and 10–18. Both are presented in the Food Safety Commission of Japan's fact sheet.
Health Canada
45 mg for ages 4–6, 62.5 mg for 7–9, 85 mg for 10–12, and 2.5 mg per kg of body weight from 13. These are daily figures based on standard body weights, presented in the MHLW Q&A and the Food Safety Commission fact sheet.
Effects on sleep
The MHLW Sleep Guide for Health Promotion 2023 says adverse effects on children's sleep have been reported at 1–3 mg/kg a day or more. For a 30 kg child it gives 30–90 mg as an example.
One cup
Hojicha infusion holds 20 mg per 100 mL (15 g of leaf, 650 mL of water at 90°C, 0.5 minutes). A 150 mL cup holds about 30 mg [calculated].
Body-weight example
3 mg/kg a day for a 15 kg child comes to 45 mg, a cup and a half of 150 mL [calculated]. That is the same amount as Health Canada's 45 mg for ages 4–6.
Swaps
The sleep guide says the caffeine in teas comes from the tea leaf (Camellia sinensis), and gives barley tea, buckwheat tea and other drinks made without tea leaves as swaps.