Children will be learning at school how to round up decimals to the nearest whole number. A fun way to practise this at home is to use regular dominos and establish that each piece is a decimal number (so a domino one with 3 dots and 4 dots is 3.4). Encourage them to play with the dominos, but with the rule that they can only, for example, join 2 dominos that are within 1.5 of each other. This will really get them thinking about what each decimal point represents. A number line can also be useful when rounding decimals.
Never underestimate how much a visual representation of what can otherwise appear to be an abstract concept can help children learn.