bake a layered cake with rainbow / flag colored layers so when you cut into it, it shows the flag
(if you're trans) give them a baby card or balloons that say "congrats! it's a boy/girl"
(if you're nonbinary) fill out one of those admission forms with personal details and include your new name with your old name in parentheses. when you get to the gender question, the boxes will be like □ girl □ boy ☑ genderless entity in human form (or nonbinary if you're looking for something more straightforward)
customize a mug or plate that says "I'm gay/bi/etc." and put coffee/food in it so when they finish, they see your message
film a tiktok with them with a song that has a very obviously queer message
buy a pride flag and have them help you hang it up in your room
put pride decorations all over your house so they see it when they get home
if you can, grab their phone and change your contact to a new name if you're trans, or (your gay/ace/trans child/friend)
buy them a shirt that says "proud parent/friend of an aromantic person"
if you're dating someone of the same gender, have them meet your s/o
if you're not feeling very confident, put a sticky note on their door/somewhere they'll see it and leave quickly
buy or make a card (like a credit card or game card, doesnt matter) with your identity and flag on it, so you can pull it out and say "I'm pulling the gay card"
"let's get one thing straight. I'm not."
put together a photo album that displays your growth, then put a picture of what you look like now at the end and have a caption that says "congrats on raising your gay child!"
casually mention it in an unrelated conversation and then keep talking like normal. if they say something about it, simply say "yeah, I am, but that's not the point. anyway, like I was saying..."
say it in a hangman puzzle
or a word search or word scramble puzzle
leave clues around the house in a mystery game
place a flyer in their windshield that says "your child is trans!" etc
spell it out in a game of scrabble (might be harder to rig)
make a card with a fancy envelope that says "we would like to honor your child as an official, upstanding member of The Gay Society"
give them a card that says "this card for lifetime membership of the LGBTQ+ Community is being awarded to (insert name) for being a lesbian. Congratulations!"
jump out of a literal closet and say "I'm coming out!"
carve it into a pumpkin and make it a jack-o-lantern. put it on their doorstep with your name attached.
I might update this later. feel free to add your own!