Kids work old school books - primary school ones are unlikely to be of any use or much sentiment in the future. Secondary ones some may prove handy if continuing study in the subject ditto more likely to prove the thing you wish you hadn't got rid of. Plastic boxes in attic/cupboard under stairs.
kids paintings? Photograph and create an online album, keep the memories but not the clutter.
all the paperwork from the last ten years in no discernible order -
Ouch! depends what it's for
Warranties etc for products you no longer own or are over 5 years old - bin!
Banking/financials you dont generally need to keep more than 5 years unless you're self-employed and it relates to the business (I'm a little out of touch here check with hmrc website). Shred properly before bin or incinerate.
Birth certs, wedding certs, divorce docs, passports and similar - really should be in a locked metal box by front door.
Contracts - for phones, insurance etc in same able as above but review regularly and get rid when superceded by new contract
toys that they all want to keep and shit loads of them - I have a clear out twice a year and been doing so since my daughter was little. 3 options - keep (and here not allowed to keep anything that irreparable, not been used in past 6 months), charity or bin. Ruthlessness is key - oh and it applies to YOUR toys too shameful serial hobby uptake who then quits here
clothes everywhere, dont even know what I have and its not all clean - 1 year rule applies to everyone, if you've not worn it in a year you're not gonna. So - bin or charity.
dvdsbooks - aforementioned 6 month rule applies to adults too, only difference with these is you can probably make money out of them - various online companies you can sell to either individually or in bulk, plus high Street places like cash converters.
Pens etc soon as not working bin.
Batteries - most supermarkets, wilkos, Argos, pound shops have recycling boxes for these please do this as theyre a real hazard.