No European country is going to go into Ukraine on a peace keeping mission, to be safe from attack and be able to respond to an attack, the numbers involved would need to be in the 10s of 1000s, supply lines set up, troop rotations, a no fly zone, warships in the black sea.
Lviv to Mariupol is almost 1000 miles!
this is cloud cuckoo thinking.
If Putin wishes to help those in Mariupol, he can have a 48hr cease fire, its simply a phone call away to his equally murderous forces.