claiming back UK tax paid for minors resident in France

[hoverfrog]

My two minor children have trust funds from my parents' estates, held and administered in the UK.

The trustees tell me that if the interest is acrued then tax will be paid on it as the trustees are deemed liable for the tax.

However, if the income is paid out for the welfare of the child then the tax can be reclaimed on their behalf.

However, my children are French resident, so:

1/ can I still claim back the tax for them?

2/ will they end up (or will I!) paying tax on this income in France?

3/ if tax has to be paid, which country takes the least?