While prepubescent children may enjoy a degree of participation in the spiritual practices in many traditional shamanic cultures, they generally are NOT encouraged to do extended personal journeys.
Why? One belief is that since children just recently arrived from that place of being merged with Spirit, their early childhood years are a time for getting grounded here on earth.
Yes, many kids "journey" naturally, but only as much as suits them before their attention shifts. The extended formal journeys we use in this format are not appropriate to most prepubescent children.
Older children (post-pubescent but under 17) are welcome if they (a) already have some formal journeying instruction and experience, (b) conduct themselves appropriately in ritual settings, and (c) parents have already cleared their participation with the facilitator.