Hi fuzzpig:
Neither of my DDs could add/ subtract numbers in their head in Y1. I think DD2 showed signs of this in Y2 but DD1 (who struggled with maths) was definitely Year 3.
Games that can help:
Snakes and ladders: Play forward for addition & backwards for subtraction. Use more than one die to generate larger numbers. We started off counting out loud (so if DD1 rolled a 4, we'd count from the space four on - so if she was on 10, we'd say out loud together 11, 12, 13, 14. And then repeat without the counting - so 10 + 4 = 14.
Another useful game we found was playing 21 or blackjack open handed. Have to teach them that face cards = 10 and ace = 1 - but basically it can be a lot of fun as a family game - spice it up by betting smarties or candies after first two cards are dealt.
We also played addition SNAP. So decide what number you want to work with - maybe 9. Face cards = 10 and ace = 1. Flip over card - say it's an 8. What is 9 + 8. You can use number line or fingers or number square - but it's a fun game (go really slow so they can win now and then). [for subtraction version - just take away the flipped card number from start number].
The other game we play is who can get the highest number. So same rules about face cards = 10 and ace = 1. Deal each player 10 cards - each player adds up their cards. You can play best out of 5, etc... - or winner chooses what's for dinner. [We used this a lot for subtraction. Everyone started with 100 and we would see who gets to 0 first].
useful on-line games:
woodlands junior school maths zone: addition games to 10, 20 and 100: resources.woodlands-junior.kent.sch.uk/maths/numberskills.html
also subtraction games from numbers to 10, 20 and 100: resources.woodlands-junior.kent.sch.uk/maths/numberskills.html
digit workout from crickweb: www.crickweb.co.uk/ks1numeracy.html - simple digit addition to 20 and 100.
ambleside primary addition zone: www.amblesideprimaryschool.co.uk/Learning-Zone/Maths-Zone/Addition.html
ambleside primary subtraction zone: www.amblesideprimaryschool.co.uk/Learning-Zone/Maths-Zone/Subtraction.html
Math Games counting games: www.maths-games.org/counting-games.html
HTH