The plot is based on two children, one Catholic, one Protestant going to the same school, however Belfast schools were segregated at the time. So this seems very unlikely.
The car set on fire at the start has the reg CZ followed by five numbers. All N Ireland reg plates had two letters and four digits.
About 1 hour 30 into the film, the scene showing the chimneys and side of houses, a satellite dish can be seen in the bottom left corner.
At about 33 minutes, a diagram of the solar system is shown which omits Pluto. Pluto was considered a planet in 1969 and would have been included in such a diagram at that time.
About 20 mins from the end, a wide b/w landscape shot shows BOTH cranes in the background.
According to Wikipedia, only one was built in 1969, the other finished in 1974.
"The cranes are situated in the shipyard of Harland & Wolff and were constructed by the German engineering firm Krupp, with Goliath being completed in 1969 and Samson, in 1974. Goliath stands 96 metres (315 ft) tall, while Samson is taller at 106 metres (348 ft). Goliath, the smaller of the two sits slightly further inland closer to Belfast City. "
According to Wikipedia, only one was built in 1969, the other finished in 1974.
"The cranes are situated in the shipyard of Harland & Wolff and were constructed by the German engineering firm Krupp, with Goliath being completed in 1969 and Samson, in 1974. Goliath stands 96 metres (315 ft) tall, while Samson is taller at 106 metres (348 ft). Goliath, the smaller of the two sits slightly further inland closer to Belfast City. "
At the time the film is set, only about a third of UK houses had a telephone. Given the apparent poverty of the family, it is unlikely that they would be among that group.
The family are shown as being 'working class' with the father having to work across the water and the grandfather not holding down a job for more than a week. However at Christmas Buddy has been given a Les sentinelles de l'air! (1965) toy and a Thunderbirds suit. Both of these were highly sought after Christmas presents costing a lot of money and outside the reach of most working class people.
In many shots a Ford Cortina MK3 can be seen on the streets. Considering the film is set around late 1969 and early 1970, the MK3 Cortina wasn't introduced until October 1970.
At about 25mins in Buddy's Pa throws a couple of brochures onto the kitchen table re. relocation to Australia & Canada. One of which is titled 'Discover a home in Vancouver Canada'. However, the cover photo features a photograph of a glacier covered mountain in the Canadian Rockies (at Lake Louise) in the neighboring province of Alberta, which is an 8.5 hour drive east from the city of Vancouver.
The accents of the characters come and go, especially for Ma.
When discussing the Apollo 11 mission with his grandparents Buddy refers to the command module as "Columbus."