I know this sounds defeatist but I stopped what I call 'serious' gardening for about 2 years when dd was between the ages of 18 mths to 3.5 yrs and resorted to buying young plants instead of raising them from seed, and took other similar short-cuts.
I probably gave up too easily but I always found that the limited time I had to garden was spent stopping dd eating poisonous plants, skewering herself on bamboo supports or falling down stone steps!!
I started again when she was nearly 4 and gave her a large raised bed/container for herself in which we plant sunflowers, radishes, courgettes, herbs etc every year and she really enjoys gardening now.
You are probably more dynamic than me though (am ancient mother) so if you go ahead would recommend investing in some sort of outdoor play pen if possible (sand pit padded with washable canvas-backed outdoor blanket instead of sand) or inflatable ring or similar???
When she is older and toddling about would recommend investing in little play house and miniature gardening set (gloves, spade, apron, boots, watering can, bucket and mini wheelbarrow if at all possible). I bought a second hand set off ebay and it kept dd occupied for hours.
In terms of clothing, see the Puddlepac lightweights
Good luck!