I've been piecing this post little by little for a couple of months now, though it was originally inspired by Galina Krasskova's "Top 10 Pagan/Heathen Movies". I've complied a list of films, books and television series which I find provide excellent stories and useful lessons for kids. While quite modern, and not necessarily Gaelic, still have some value as widely available media to instill virtues and concepts which are pertinent to GRP's (and perhaps polytheism in general).
A quick side note: Krasskova's overviews of both "Princess Mononoke" (Mononoke Hime) and "The Lion King" are excellent and I need not repeat them here. They are, however, some of my favourite animated films and can not recommend them highly enough.
I will however, mention Hayo Miyazaki's "Spirited Away" (Sen to Chihiro no Kamikakushi). The story is simple enough, that children will thoroughly enjoy it, but the issues are complex enough that adults will find much to contemplate. The premise is the synthesis of modernity coming to terms with the past/ environment which is a hallmark of Miyasaki's style. In this instance, the main character, Chihiro, finds herself having to survive in an other world inhabited by the Kami of Shinto lore, with nothing but her will and the support of a few sympathetic Kami who aid her. It has very clear environmentalist overtones, but it is also tries to impart the importance of folk tradition in a world where so many are utterly disconnected from it. There is actually an excellent essay, "Forest Spirits, Giant Insects and World Trees: the Nature Vision of Hiyao Miyazaki” by Lucy Wright, which I came across (thanks to Finnchuill's Mast) which explores the way Miyazaki utilizes elements of Shinto in his films.
A novel series I discovered last year, is the Warrior's series of books. The books follow several clans of anthropomorphic cats, and chronicles the political and social turmoil between the clans. The great thing about these books are the various virtues they impart, in a way that children can understand and, perhaps, emulate: honour, courage, loyalty, living in harmony with local geography and reverence of ones ancestors. The warrior aspect is very apparent (it is after all the title of the series), but the inclusion of ancestor worship, as well as the "mystic experience" was something which is absent in a lot of similar series. The ancestors are referred to as "Starclan", and this is the closest thing to a religion which exists in the Warriors world. While not Celtic or Gaelic by any stretch of the imagination, it none the less is a way for children to develop a sense of the significance of ancestor reverence and virtues like honour and courage, while being accessible and enjoyable.
A cartoon series I would heartily recommend is "Avatar: The Last Air Bender" (and not the insipid live action film version). I will try to keep the fan boy gushing aside, but this is simply one of the best animated series I have watched. Period. There are some aspects to the show I do not like as much as others; the heavily pantheist leanings chief among them, and the emphasis on detachment from the world. There is, however, much which can be taken from the show. The interaction with the "spirit world" and local land spirits is a decent representation of more traditional forms of animism, fairly reminiscent of Shinto. While often side stories to the main plot, "trips to the spirit world" are always of benefit to the progression of the plot and the character development of Aang, the aforementioned Avatar. The way the spirits are portrayed cover a broad spectrum; some are beneficial, some are indifferent (unless crossed) and others are malicious. I like this aspect because it is more reflective of the way GRP's understand interactions with the fair folk or spirits of place, and avoids the sunshine and sprinkles approach which is fairly prevalent.
There are some other aspects of the series I also think admirable. The way that issues of morality are explored are multifaceted and complex enough to avoid the sort of dichotomous kinds of morality so often found in works of fiction. A good example of the later is found in the Redwall series, which I love dearly, but it operates on a very simple moral framework. There are competing perspectives in the Avatar world, and it seems like the writers went out of their way to not, necessarily, have one tack superior to another. Aang, the chief protagonist was raised by Monks and so has a considerably different approach to morality than another character, Katara. The best example I can think of has to do with the idea of forgiveness. There are some spoilers ahead, so if you haven't yet seen the series or are in the process, skip ahead.
In the episode, Katara learns that Zuko (a former enemy turned ally, who she is currently having some trust issue with) can help her find the man who murdered her mother. As they prepare to set off, Aang tries to talk her out of it, extolling the virtues of forgiveness and how seeking vengeance will only hurt Katara in the long run. She ignores him and long story short, confronts the man who murdered her mother. Seeing how pitiable his life is, she can not bring herself to kill him, and returns. Aang, overjoyed that Katara has forgiven the man, is corrected by Katara and is informed that she will never forgive him, but can forgive Zuko.
[Spoiler warning ends]
The approach to the issue of forgiveness is one I can really appreciate, because the idea of automatic forgiveness is something I strongly disagree with. Restitution needs to be earned by those who have transgressed, and it is unreasonable (bordering on unethical) to expect someone who has been seriously wronged, to forgive those who have wronged them automatically. I understand the general cultural significance of forgiveness, and its basis is a different religious perspective, but that doesn't mean I need to agree with it. And therein lies the beauty of the series approach to morality, characters can be ethical without believing the same things or having the same foundational basis for moral action. Whats more it manages to deal with issues like morality and ethics without being pedantic or clumsy, which is something which can not be said about a lot of other children's shows.
I'll probably post some more suggestions at a later date as I either remember them or actually add new ones to the list.