Hi Miketrixtunes
Welcome to the Apple (user-to-user) Community.
Thank you for starting a discussion in the community.
Re: Child's Apple Pay declined at stores
Wondering if the particular stores have limits on purchases :
eg: only cash for under $5 or under $10 purchases.
and
whether purchases over $10 have been made / accepted using Apple Pay
Also: some stores may not be set-up to use Apple Pay:
Your teenager may need to look for the correct symbol(s) displayed in stores
Learn where to use Apple Pay - Apple Support
And: To ensure your teenager's device is compatible with Apple Pay:
Devices compatible with Apple Pay – Apple Support
Else:
If Apple Pay is really not working:
You may want to use online chat, phone, or eMail etc. to Apple Pay Support:
There is a "Get Support" link at the bottom of their website (link below).
Apple Pay - Official Apple Support
All the best :-)