First-time visits go a lot smoother when nothing catches you off guard. Here's what a typical federal visit actually looks like.
Security screening
Expect a metal detector and possibly a pat search, similar to airport security but for a visiting room. Bring a valid photo ID for every adult visitor -- you won't get in without one. Kids usually don't need ID if they're young, but check the specific facility's rules if your child is a teenager.
Dress code
BOP's standard is "appropriate for a large gathering of men, women, and children." Concretely, that means no: revealing shorts, halter or crop tops, see-through clothing, low-cut blouses, sleeveless tops, miniskirts, backless tops, or anything that resembles what inmates wear (often khaki or a specific color -- check the facility page). This applies to visiting kids' clothing too, within reason -- normal children's clothes are fine.
Physical contact
Generally: a brief embrace and kiss are allowed at the start and end of the visit only. For the rest of the visit, hands need to stay visible, usually meaning on the table. This surprises a lot of kids who want to sit on a parent's lap the whole time -- worth explaining in advance so it doesn't feel like a rule they're the only one breaking.
What to bring
Usually just ID and maybe quarters for vending machines (common at many facilities, cash often isn't otherwise allowed inside). Outside food is typically not permitted. Confirm specifics -- lockers, what you can carry in, exact hours -- on the facility's own page here before you go.