Cool!
I had aquariums as a kid, and get back into it now and then. In a big way at the moment.
My brother and I collected baseball cards when we were kids. He recently read an article about Topps and decided to start buying some cards this year (they’re doing neat stuff for their 60th anniversary) and now he’s got me buying them and we’re trading and doing stuff online and everything.
But there has been about a 20 year gap in our collecting.
Cartooning, drawing, writing, performing (theater, magic, puppetry, clowning), reading.
I don’t know that I’ve ever fully abandoned any of my early hobbies.
I still collect rocks.
I still love photography.
I still love exploring places I shouldn’t go - abandoned factory’s, houses, barns etc…
I’ve done needlework since I was a child. And reading, of course.
Reading. Pressing leaves and flowers flat in a big book. Birdwatching. Later in childhood, around 12, my seamstress grandmother got me into sewing, and I still sew on occasion. I still spend a lot of time in a fabric store, poring through the pattern books and looking at bolts of fabric - sometimes I bite the bullet, buy a pattern and material, and have at it (but its usually for someone else who needs a cool sleeveless dress for summer, or a pencil skirt in a herringbone wool.)
Tennis
Mostly photography. My mother got a little tired of hauling me around town on Sunday morning so I could take pictures of urban decay or rabid wildlife, but I guess she figured there were worse things a kid could be doing. I eventually put some of the photos showing the changes in the town where I grew up on the Internet.
I also painted and still do. And I wrote–generally poems and stories about terrorists, paranoics, or paranoid terrorists. I keep that up from time to time.
Reading - anything and everything, all my life.
My husband loved toy trains as a child. He is 91 now, a Master Model Railroader, and he has a huge model railroad in our basement. 
I wish I had been into something practical or useful like this. Mine is reading, and it’s brought me a great deal of joy, but it’s been of no use to anyone else.
I also used to draw and do various crafts. It doesn’t really fit here because I don’t have time anymore, but I might start it up again someday.
I started camping as a Cub Scout and with my family. I have never stopped (just got back from a week in the high country of Yosemite).
I loved my dolls and dollhouses.
So now I play Sims.
Kinda lame, I know. 
Theatre
I think I got my first part in a community play when I was in grade 2 or so. I acted in every school play and community theatre production I could. Now I earn my living working on plays. I work behind the scenes now and havent been infront of an audience in almost 10 years.
D&D. Video games. Reading. Crossword puzzles.
Actually, it would probably be a shorter list if you asked: “What hobbies do you have now that you didn’t have as a kid?”
my mom told me i shouldn’t do that anymore.
still read, learn, fix stuff, build stuff, move electrons.
Reading, according to my mom I was a very early reader and I’ve never stopped.
Baking, I started out on an Easy-Bake oven when I was probably 6 or so.
Counted cross-stitch, my aunt taught me when I was about 10 and I still do it sometimes, but not as much now that my eyes aren’t as good. 
Needlework/embroidery: started when I was around 4-5 yrs old, before I started school; I picked up counted cross stitch when I was in high school.
Crochet: started in elementary school
Reading: learned in Kindergarten and haven’t stopped enjoying a good book since
In 1977 or 1978 my dad started bringing home a DEC Silent 700 terminal from work. He answered my curious questions and allowed my brother and I to log in to his work account (with the telephone planted firmly in the “acoustic coupler muffs”) where we would simply goof around.
But I was curious, and so by fifth or sixth grade I was learning how to use the Teco text editor and Runoff (a markup language for document layout). My brother and I started playing around with BASIC programming, learning our way by looking at other programs we found on the system.
My dad really knew nothing about programming, so he gave us no guidance whatsoever.
By middle school, in a world of grownups who were mostly innocent of anything related to computers, I was that one geeky kid turning in his homework on greenbar paper.
In ninth grade my mom gave me a VIC-20, in exchange for silencing my ham radio broadcasts forever (and thus silencing the neighbor’s complaints), and I continued my love of programming, eventually writing 6502 assembly code by studying the list of op codes provided in the very thick and comprehensive owner’s manual.
And I still write software today, though I am paid for it. Life is good when you can follow your childhood hobby and have people pay you for it 
I’ve had the same hobbies almost all my life: keeping/raising pets, which has many aspects which can take up your time (dogs, fish, and cats have always been my thing, but I also had rodents for a while there too, which I don’t currently), gardening, computer games, reading, cooking (I was always a big baker but now I don’t eat baked goods, so not so much unless I can give it to someone else).
The only thing I stopped doing now that I’m an adult is obsessively making things out of clay. But I still break it out now and again.
Draw, draw, draw. Paint, paint, paint.