Childcare is more expensive here because we pay too little tax to fund most public services properly, in my opinion. This doesn't mean grandparents should foot the bill directly though.
If you have to choose to follow a career or stay at home with children there are always going to be sacrifices. If someone is paying half their wages in childcare it does at least mean that they take half home, unlike my friend years ago who had childcare costs which left her a few pence in defecit at the end of the working week! She thought it was worth it though to 'keep her hand in' and was lucky to survive for two years with just her husband's meagre income.
I don't think I would suggest paying childcare. If money is tight, do what my parents did for us - pay for some decent shoes now and again, cover fuel/travel costs if visiting from a distance etc. These little bonuses mean that families on low incomes have lovely 'breathers' in the hard work of day to day living. These practical 'treats' we're really great - gifts of love and recognition, it felt, of the efforts we were making to bring up our little family on a very modest income.