This answer is given by Alistair age 6, from Impington Infants School.

For the two digit numbers I took each number less than 6 and worked out what number would have to be added to make 6. These numbers have digits which add up to 6:

15
24
33
42
51

Here are Alistair's 3 digit numbers:

114
123
132
141

213
222
231

321
312

411

For each combination of digits, I made sure that I included the same digits in different orders.

1113
1122
1131

1212
1221

1311

2112
2121

3111

11112
11121
11211
12111
21111

111111

There are no 7 digit numbers because 7 is over 6 and we are not allowed zeros.

Well done Alistair! You have gone about this very logically. There is just one number missing. If you can spot it, email us to let us know.