Journey for Margaret (1942) starring Robert Young and Margaret O'Brien. Although Margaret O'Brien took her professional name from this film, to my knowledge it is rarely seen. It was on TCM last night and previous to that I had seen it only once, about 25 years ago.
The Boy with Green Hair (1948) starred Dean Stockwell in an early role and was Russ Tamblyn's first movie.
Forbidden Games (1952) is a French film set during WWII in France.
A War of Children (1972), about how the troubles in Northern Ireland affect two families, stars Jenny Agutter, previously of The Railway Children and later of Logan's Run.
All of these are powerful anti-war statements depicting the effects of war on children. The Boy with Green Hair turns up occasionally, like on St. Patrick's Day. Forbidden Games I think I've seen twice in forty years, both on Public TV.