I think it is a good idea of jingls to make some party food and have a little party when your DGS is brought round to see you to 'pick up his present'. Could you speak to your son - very nicely - and ask if he and your DIL would like to pop around and stay for a cuppa and a piece of cake on that day and mention that you would like to have a little party with DGS (you don't want her to get upset if he eats cake, crisps and jelly at your house then won't eat his nourishing dinner later!). She can always say 'no' but at least you have tried. If she says no, just say 'oh, OK then, I expect you are busy' and leave it at that.
Just try to have a fun hour or so with your DGS and DS and don't say a word about missing the children's party (which could be noisy and not everyone's cup of tea).
She obviously has a few problems if she doesn't see her own mother - perhaps she doesn't realise how nice you are! 
I need advice for a mutually messy situation
Can anyone recommend a non sticky body lotion?


. Sundried didn't say she was expecting to be invited, she simply stated that her son had told her she wasn't going to be.
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