What is happening here?
In Grade 4 children meet the decimal point properly for the first time: in money ($3.45), lengths (2.35 m), weights (1.75 kg) and capacity (0.5 l). Decimal numbers as a topic of their own come later. For now the point is to understand the decimal point as a divider between two units.
$3.45 is 3 dollars and 45 cents. 2.35 m is 2 m and 35 cm. Your child keeps calculating with whole numbers, just in two units side by side.
What helps at home
While cooking and shopping, have your child read and convert amounts with a decimal point: the package says 1.5 l, which is 1,500 ml. The receipt says $2.80, which is 280 cents. The more often your child switches between the two ways of writing, the surer it gets.
Maps and city plans work well too: a scale of 1 : 20,000 means that 1 cm on the plan is 20,000 cm, so 200 m in real life. Measuring the way to school on the plan and converting it to meters ties measures and scale together in a concrete way.
What can go wrong
The classic mistake: 0.5 l is read as 5 ml. The mental picture helps here: half a liter is half a bottle, so 500 ml. The same goes for $4.05: that is 405 cents, not 45. The zero after the decimal point belongs there, it keeps the tens of the cents place free.
And as always: a number without a unit is not an answer. "1.75" alone says nothing, "1.75 kg" does. Writing the unit along avoids most mistakes right at the writing stage.