For our son's birthday, we wanted to do something a little extra, so we got a helium tank and inflated helium balloons.  It was a big hit!

These Cars balloons inflated well for us:

And because our little (big) guy turned six, we got this which is still flying high in our house:

We've had a lot of fun with regular balloons, and a balloon animal kit during this lockdown.

I also have a lot of fun being "Captain Balloonhead".  I'm a Disney villain with a ridiculous voice, who puts a balloon on top of my head and gently bops the kids with a balloon in my other hand.  I go on about how nobody can defeat Captain Balloonhead.  They love it!  They eventually knock the balloon out of my hand and win (natch).