Table 1 Sample characteristics: (1) frequency of exposure, and covariates in the sample and (2) prevalence of mobile device screen use ≥ 1 h by covariates

Age (n = 31,125)

p < 0.001

2 years

15,472 (49.7)

7,5

3 years

15,653 (50.3)

12.3

Child gender (n = 31,125)

p = 0.002

Male

15,916 (51.1)

10.4

Female

15,209 (48.9)

9.4

Family educational level (n = 30,635)

p < 0.001

Short^b

12,851 (42.0)

11.8

Medium^c

8584 (28.0)

9.3

Long^d

9200 (30.3)

7.6

Parental employment status (n = 28,613)

p < 0.001

Both parents work

19,000 (66.4)

8.6

One parent works

7780 (27.2)

12.3

No parents work

1833 (6.4)

13.3

Migration status (n = 28,741)

p < 0.001

Both parents of Danish origin

21,455 (74.7)

8.6

One parent of Danish origin + one parent immigrant or descendant of immigrants

3240 (11.3)

9.7

Both parents immigrants or descendants of immigrants

4046 (14.1)

16.9

Mobile device screen time during a normal weekday (n = 31,125)

No screen

8664 (27.8)

-

< 1 h

19,373 (62.2)

-

1–2 h

2669 (8.6)

-

> 2 h

419 (1.4)

-

TV/PC screen time during a normal weekday (n = 31,114)

p < 0.001

No screen

3732 (12.0)

13.4

< 1 h

22,251 (71.5)

5.7

1–2 h

4471 (14.4)

23.7

> 2 h

660 (2.1)

40.6

Reading to the child (n = 31,125)

p < 0.001

Daily or almost daily

20,213 (64.9)

7.7

A few times a week or less frequently

10,912 (35.1)

14.1

Mental well-being (n = 31,125)

p < 0.001

High (WHO-5: ≥50)

27,001 (86.8)

9.5

Low (WHO-5: <50)

4124 (13.3)

12.8

Parental preoccupation with smartphone (n = 30,979)

p < 0.001

0 indicators of high preoccupation with smartphone

20,291 (65.5)

8.6

1 indicator of high preoccupation with smartphone

8421 (27.18)

11.7

2 indicators of high preoccupation with smartphone

2267 (7.32)

15.0