Hard risk : You sent message immediately after you follow, you even don’t wait for weather they like your account or not. By doing that your mother account will get too many spam reports.
Low risk : You just follow them, and you’ve put promoting link everywhere like in bio or in your post. They think it is pure spam, so they will report your child account plus your main account.
No risk: No more hard promotion, not more link in bio…just quality post which is related to your mother account and you’re good to mention your mother account.
Plus one main thing, do not follow same accounts on other child account, they will think it is similar account and will report all your account.