I don’t think it’s bullying, because bullying involves tormenting them - finding what they react negatively to, and pushing on that. Here, you’re letting them know that there’s something you need them to do before you’re comfortable playing with them. You might think of it as modelling how to protect your own bodily autonomy!

For me, when my kids were going through that, I’d say something like “Ack! Don’t touch me with poo hands! Go wash first, then you can climb on me!” It’d generally get a giggle, then they’d go finish washing up. You’ll want to pay attention to their reaction whatever you do, but if you make it clear they’re still welcome to play, I don’t see how it could be bullying.