The first time I went up Seefin I followed a track from the west. It was wet, mucky and not at all family friendly.
Thinking it would be good to share the joys of the cairn with the kids, I have since found that the easiest route is definitely from the South, and it makes for a nice family walk.
The start point is actually at O 06831 14489, so don't be fooled by the false start at Kippure Centre here. Our initial route with small ones was blocked by a stream crossing.
Park at O 06831 14489 and head east along the forest track (to the right as you cross the barrier, then loop back west before heading north along an easy track.
Very pleasant outing that can be enjoyed by all the family, the cairn an obvious attraction at the summit.

If in the vicinity I always like to head towards the Sally Gap to get a look across at the Coronation Plantation, the kids reckon it looks like somewhere in Africa, the sparse covering of trees contrasting against the yellow moor grass. You can also ramble across to the Obelisk and see the trees at closer quarters, see track 1685.
Though I'm easily pleased, even the autumnal colour in the beech trees as you head east after Cloghleagh Bridge is enough to warm the cockles of the heart!